Ok so I know this is probably covered somewhere but I've been searching for a while and I just need a quick answer. I have Sonar Producer 7 with an ASIO driver. Under Options->Audio my mixing latency is 4.4 msec, the buffer size is moved all the way over to 'Fast', and I can't adjust it as it is greyed out. Now, when I have a normal project with Audio and Midi tracks and softsynths I get NO latency between the time I hit the keyboard key and the softsynth output. But now I have a project with multiple busses, each with their own audio effects, and I route all of my audio tracks to these busses. Now on the MIDI tracks with softsynths, I get a latency between the time the key is pressed and softsynth output. I assume it's the busses and their audio effects. Is there a way to remove the MIDI latency?

It's basicly up to your computers horsepower and soundcard drivers how low you can get the latency.
In almost any system, though, you can reasonably easily get to the limits of your system, as many soft synths and FX are really CPU hungry.

So without knowing your systems specs nor what VSTs you're using, it's hard to speculate anything. It's normally street wise to add the heaviest VSTs only after all the tracking is done, or keep some of them disabled when not auditioning/tweaking the sounds. During mixing you can set the latency how high you need to, because it doesn't matter.

Some plugins add noticeable (and unavoidable) latency, and most of the ones that do are the types you'd most likely put on a bus: linear-phase equalizers, convolution reverbs. Leave out bus effects (including Ozone) until you're done tracking.

I always use the "Global Bypass EFX Bins" when recording new MIDI tracks, otherwise, latency. Quick and easy.