I tried using these plugins on a track.  After about three measures of playback the timing of various tracks was off and just kept getting worse.  I read some posts about these being CPU hungry.  Literature says they are 'high quality' plugins, but can one obtain similar quality without them?  I'm trying to get best mix I can with stock Sonar plugins.   
 
And there are plenty of other plugins.  The Nomad Factory suite and the PX64 / VX64 / VC64 presets are nice for a newb like me and to my ears they work well.  The Pro Channel modules are there too.
 
Maybe I answered my own question  Thoughts?   

No they're not necessary. You can get great results without them. In fact, I prefer NOT to use multi-band compression. Neither one gives my computer any problems, and they're perfectly good plugins, I just choose not to use them.

imo those are 'mastering level' plugins whose role is best for the entire mix.  u didn't say how u used them.  when using plugins, there is always a point where they begin to overwhelm the system... you can try to increase the buffer size, but looking at your system and the external sound device will no doubt cause issues at some point, depending on the plugs used.  heck, I've created some huge projects and if you try to throw in a 'demanding' plug that has it's own latency, there will be issues.  I use those on some mixes and may notice some increased demand, and may need to tidy things up by freezing a synth or rendering a track with lots of plugs to reduce the demand. 

All EQs are not designed to fulfill the same function. Some are designed to have "character," some emulate classic designs that had their own charms (like the Pultec EQs), some are designed for transparency, others are best for "surgical" precision where you need to make extremely detailed frequency response edits.
 
The LP types are phase linear, which means they are designed for transparency. As a result, they are very good for mastering because by that point, you probably did any coloration in the mix, and simply want to alter response in some way. I've done tests where I set the LP EQ and Sonitus EQ to the same settings, and you can hear that the LP is a bit more transparent at the higher frequencies, so it is an audible difference.
 
I prefer the ProChannel EQ for individual tracks because of the various options - I can pretty much find whatever I want. I use the Sonitus for "utility" applications, like dropping midrange going into an amp sim, because they're very flexible (lots of bands!) and have a low CPU hit. The LPs get put in the master bus, if needed.

Thank you all for the education, most valuable. 

olemon
Thank you all for the education, most valuable.

Cool...click the "helpful" button so others can find it

Not strictly related but last week I asked "What is the best Multiband compressor?"
http://forum.cakewalk.com/What-is-the-best-Multiband-compressor-m2958766.aspx
 
I got some great answers... the reality is the LP64 is pretty darn good anyway.
Hope this helps.