Just for haha's I did an experiment with MIDI tracks.  With a blank project my memory usage was 8.0 GB (I had other things loaded prior to this).

 
 
 
 
 
I then added 1015 MIDI tracks containing 3 bars worth of MIDI data.  After 1015 track my memory went up to 8.7 GB.  
 
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I hope this table below makes sense!
                    
Description           Total Memory        Working Set    CWP FILE    MIDI FILE
pre-launch               1.15 GB                0 KB        
launch - no project      1.29 GB          111,628 KB        
blank project            1.49 GB          129,116 KB        
normal project(10 buses) 1.65 GB          279,216 KB        
1 MIDI track             1.65 GB          288,120 KB        
50 MIDI                  2.02 GB          678,240 KB        
100 MIDI                 2.40 GB        1,077,528 KB    1,049 KB        3 KB
200 MIDI                 3.17 GB        1,879,444 KB    1,807 KB        5 KB
400 MIDI                 4.69 GB        3,477,648 KB    3,334 KB        10 KB
800 MIDI                 7.24 GB        6,672,600 KB    6,390 KB        20 KB
end Sonar                0.94 GB                0 KB        
blank project (no buses) 1.07 GB          149,552 KB        
1 audio track            1.09 GB          140,608 KB        
50 Audio                 1.41 GB          545,804 KB        
100 Audio                1.54 GB          560,396 KB       692 KB    
200 Audio                1.94 GB          981,916 KB    1,136 KB    
400 Audio                2.74 GB        1,813,580 KB    2,624 KB    
800 Audio                4.39 GB        3,475,128 KB    5,200 KB    
end Sonar                0.95 GB                0 KB        
200 MIDI + 200 Audio     2.77 GB        1,965,820 KB    3,255 KB    
400 MIDI + 400 Audio     7.32 GB        6,704,248 KB    6,231 KB    

The bottom line is that a file with 800 MIDI tracks uses 7.24GB of system memory, and the Sonar image itself uses 6.67GB of that total. THe actual file size remains a modest 6.4KB as a CWP, and an embarrassingly tiny 20 KB for the MIDI file.

I wasn't clever enough to figure out how to post a file here, so I'm including a link to a zip file that includes all of the CWP and MID files I created. If anyone has the time to open these files I'd appreciate it if you can verify my results... or tell me I am delusional!

And thanks all - I really do appreciate the assist!

Hey Bill 
 
I opened them with no problems.  The 800 MIDI tracks opened and I went from using 8.1 GB pre-launch to 8.7 GB memory used,  (I had other stuff in use on computer prior to launching, which explains why I had 8 gigs of RAM in use already)
 
My results were similar to the original results I posted previously.  I am not getting the same results as you.

Here are the numbers on my machine, Win7 64bit 12GB RAM running X3e, opening the "800 midi tracks.mid"
Memory use reported by task manager performance tab:
Before loading X3 = 3.41GB (yes there was a bunch of other stuff running)
After loading X3 = 3.46GB
After opening "800 midi tracks.mid" = 3.78GB

So either I am doing something really dumb, or there is something very strange about my computer.
 
This is good news, really, means there is hope, but I have to do some digging! If anyone has suggestions I am all ears... and thanks for checking those files out for me!

I did not try any file other than "800 midi tracks.mid" which was accessed by File > Open inside SONAR.
 
Maybe re-personalizing SONAR by holding CTRL and SHIFT while starting SONAR will solve the problem. This will overwrite the files in C:\Users\yourUserName\AppData\Roaming\Cakewalk\yourVersionOfSonar and restore some of the registry to factory defaults. Make a copy of the user directory prior to re-personalization if you have customized master.ins, the ini files or any thing else in the user directory.

I don't get how you could possibly describe 718 midi tracks as "not a lot, really", even considering many would be triggering sample libraries on different machines. I have a really hard time thinking what kind of project would need this. I don't usually go above 100 tracks total (let alone just midi) and if I'm honest it'd be lower if I didn't keep so many ideas and backup tracks around. I can't imagine it's actually easier to navigate that many tracks than it would be to just set up the tracks when you need them. You can only really program or play one at a time anyway. Genuinely interested what kind of class this is and what the philosophy is behind such a gargantuan template.

It was said that in the Batman soundtrack, Zimmer had close to 1,000 tracks!
 
I haven't ever gotten close to that, but I could see where you might in a long production.  For instance, just 1 violin line may contain 3 or 4 samples just to make it sound realistic.  An attack (sample) - sustain - vibrato and crescendo (samples). There are different ways to treat a line like this, but I prefer different tracks for each sample in the piece.  
 
Now if you compose 25 cues in a film and lump them all together on the same timeline for post production, you will certainly end up with a lot.

Loaded sonar, Ram usage: 1.8Gb
opened 800 midi tracks.mid, Ram usage at : 2,1Gb

Closed sonar, and started it again, Ram Usage : 1.9Gb

opened 800 midi tracks.cwp, sonar responded a bit slow (not responding ) for a min
then it asked for E:\DOWNLOAD\memuse\Audio, does not exist ( its where i had the memuse folder/files)
would you like to create it ( i select no ), then it ask me to locate wavedata Directory
( i select Cancel), then i get a missing plugin (console emulator Bus) i hit ok.
then it report missing midi ports ( dakota Port 1) i hit cancel.

Project is now open, Ram usage: 2.5Gb

Closing sonar and open it again... Ram Usage: 1.9Gb


My question is rather, why on earth do u need more than 16-32 tracks of midi, that i don't understand 

My PC is old, but it runs good enought.

Maybe the issue can be related to a Graphic card as well
i did a test creating  ( insert multi midi tracks ) 96 at bulk, up to 580 tracks

What i noticed was: when i reached above 400+ tracks , they started to add slower and slower

Well fun to try out ...., but will i ever go beyond 16 midi tracks ! almost certainly not..

didn't mean to cause confusion!!
 
So why do I need 800 track? I don't... yet, but the goal is to reach that point<G>...
 
I do need about 400 MIDI tracks, and probably the 400 corresponding audio tracks, but my machine won't do that, so this is, at some level, just a bit of prep work..

Why does anyone need 800 tracks? Simple, they have 800 sample instruments loaded - almost certainly on slave machines, but they are still real.

And why does someone need 800 sample instruments? Because that's what it takes to create the best possible mock-up today if you choose to avoid key-switching. If you like key-switching you can cut this down significantly.
 
For strings, for example, you'll likely have the following groups:
solo violin
1st violin
2nd violin
solo viola
1st viola
2nd viola
solo cello
1st cello
2nd cello
solo bass
bass
violin ens
viola ens
cello ens
bass ens
strings ens
 
For each of those you'll have arco, marcato, staccato, sordino, pizzicato, bartok pizz, spiccato, harmonics, legato, and maybe half a dozen accent articulation. So for strings alone that's a dozen articulations for each of sixteen different groups, or 192 tracks Again, key switching would reduce that to sixteen tracks, which is one thing I do to economize. BUT... that's just one library, now add a second string library and you could find yourself nearly doubling that. (not every library includes every articulation - part of the reason one might have more than one string library) UGH!
 
So that's the why - in terms of producing music for media it's a very fast and efficient way to work. Everything is always at your fingertips.