This is a very general question to help get me pointed in the right direction. I'm trying to determine if I should be blaming my interface, my computer setup, or basic settings within Sonar X2 (well, I just updated to X3).
 
1) My interface (Alesis IO26) is not exactly high-end. But it gets the job done, without crashing or giving me too many problems. I also use an older PreSonus Digimax LT through the ADAT connectors to allow for a total of 16 simultaneous audio tracks.
 
2) I get high latency when tracking audio, as well as MIDI / soft-synth tracks.This is true whether I'm recording 16 tracks or 1.
 
3) I'm not worried about "audio", since I monitor through the interface. (Though, it would be nice to record a guitar track in close-to-real-time using a software amp sim).
 
4) I want to improve soft-synth / MIDI performance.
 
5) MIDI/synth latency is almost OK, as long as I'm just "parked" on a record-enabled track. Once I hit "record", latency becomes a real problem.
 
6) My "C" drive (HDD) has the OS and Samples. My "D" drive (SSD) contains the active project files (except for samples).
 
Where do I start? Is there any reason to believe a new interface would address the issues? Sorry for lack of specs.

HAve you tried the legacy FW drivers.  That helped w/ my TC Konnekt 48 on Win 7.  Also disable wireless etc.  There is a whole host of tweaks (or twerks?) to improve performance, but w/ your computer you should be fine.  So it is probably the drivers for the Aleiss.  The unit is old in interface years - kinda like dog years.

Thanks AT, that's what I was looking for. I've only used the current drivers with this particular computer. The interface had the same issues on my last 32-bit XP machine (and I tried all of the available drivers).
 
I do intend to get a new interface - I've only just begun that quest! Thanks again, Gregg

Replacing your interface will probably not have a significant impact on latency. Except for certain poor-performing devices, the hardware and its driver are perhaps third or fourth or even fifth on the list of things that determine latency.
 
The size of your buffers tops that list, along with the sample rate. The smaller the buffers (and the higher the sample rate) the less latency there'll be. However, as you make the buffers smaller (or raise the sample rate) the CPU has less time to process data between buffer cycles until at some point it cannot keep up. Then you get interruptions in the data stream, otherwise known as glitches, clicks, pops, or dropouts.
 
The best strategy is to free up the CPU so it can handle smaller buffer sizes. That means holding off inserting effects until you're done tracking, freezing previously-recorded virtual instruments, and making sure there are no unnecessary processes running (e.g. network interface or anti-virus software).
 
All that said, you might get a little improvement with a higher-end interface. Some interfaces, and I think that may include yours although I don't know for sure, have an extra "safety buffer" built into the device. This adds a fixed amount of latency that, most of the time, is not noticeable except when you're shooting for ultra-low latencies. Some interfaces that have a safety buffer allow you to disable it. Check the Alesis documentation to see if a) it has a safety buffer and b) whether it can be disabled.

Thanks Bitflipper. I can't recall where my buffers are set now, sample rate is 48kHz.
 
I've only stayed at 48kHz because it's what I've always done. I should've switched to 44.1kHz years ago. I try a couple things and see if it improves. And I can definitely freeze tracks, or rely on stems to lighten the load (while the raw tracks are temporarily archived). 
 
Still, my interface needs an update - I'm afraid it's gonna turn to dust one of these days.

I have to bypass all efxs bins when recording MIDI. Certain efx that "look ahead" are real bad. 
I was going nuts wondering why the latency was fine sometimes and then terrible others when someone else on this forum mentioned this to me. 

GMGM
 
...
5) MIDI/synth latency is almost OK, as long as I'm just "parked" on a record-enabled track. Once I hit "record", latency becomes a real problem.
 

This is a possible sign of the situation described above by Cactus (lookahead EFX). Also, be sure you are using the latest drivers (June 2010, V3.5.3.8671).

6) My "C" drive (HDD) has the OS and Samples. My "D" drive (SSD) contains the active project files (except for samples).

If you have the time & the inclination, you would benefit from swapping these around so that your OS & Samples are on the SSD and your projects on the regular HDD.
If you have a LOT of samples it will benefit to have these on a 3rd drive - preferably another SSD

This is why I love this forum! Here's some feedback...   (keep in mind at I'm not at my day job, operating from memory)

1) Safety Buffers - I can't find any documentation. This is a DICEII unit (I believe there was a patch for Sonar 6 or 7 to help DICEII compatibility, and I've always used TI chipset per recommendations).

2) Regarding FX bins, I tested a project with a single track, no FX plugins, etc. Again, I got lowish latency while simply "armed and ready", but larger latency once I pressed record and started to roll.

3) I also tried a few different soft synths, using both small and large samples. The same basic issue persists. I'm sure there's a marginal difference due ot the soft synth used and sample library.

4) SSD has been good for my audio drive (allowing higher track counts and faster bounce times). But I've waiting for my PC's warranty to expire before installing an SSD system drive (within the next few months I believe).

5) I'm also using the current drivers on my new PC. I have not tried the previous 64-bit driver though.

6) This one here might the key to it all. In X2 and before, there's a check box for "Use Self-Reported Latency" (or something very similar) within preferences. I had this box checked, and it shows 1500+ milliseconds in parenthesis behind it. I have not installed X3 yet, but I noticed that reference manual doesn't show this option (or it has been renamed / relocated). I imagine that setting is probably overriding any other parameters I've keyed in. I'll test this tonight when I have more patience.

Tbh, I'm in a similar rut. (Hopefully I'm not hijacking this thread) my latency had been lovely- unnoticeable, I'm fact. I moved up to X2 Producer and it was STILL great for a month.

It suddenly just got worse recently; even with 64-bit (is that the unit??) buffer size and getting rid of excess stuff, some audio all of my midi gets literally 1/64th earlier than it should be.

It eliminates the ability to play stuff live thru synths for practice, and it takes a lot more processing than it did before.

[mind you I'm using my headphone jack on my PC to listen, got dat ASIO to above latency]