I have upgraded to Sonar X3. It's actually pretty good. Working excellent on my machine. I was on X1 before and didn't upgrade to X2 cause I don't think it was worth it. People aren't stupid. They just put all the bug fixing together and called it X2. WTF? Ok, ok, they threw in R-MIX and Breverb but I was not convinced on the upgrade price.
But with X3, things are different. There is change in overall attitude of CW and their employees. They are very pro-active now. Fixing bugs pro-actively. Can you believe X3C update is due end of this month? Noel (CTO) confirmed that it will have updates/features that user requested. I can't believe they have started listening to their user base? I think Gibson take over did the trick.
Anyway, I am really impressed with X3. After installation what I usually do is open some heavy projects and adjust the ASIO buffer until it plays smoothly. In earlier versions it always stuttered and my ASIO4ALL buffer never came down from 512. In X3, I tried it differently just to check whether their claim is true or not. I just set the ASIO4ALL buffer to 256 and ran a heavy project. My oh my, it played so smoothly, I couldn't believe my eyes and ears. These are just initial impressions cause it's only been one a week or so. I haven't used it extensively. Just playing around and checking a few different things that's all.
I have heard on some systems it runs smoothly and on some it doesn't. Hence try the demo when it's released to check if it works on your system or not. I am not a fanboy, I just use what works for me. In fact, I have been using Reaper for last 7-8 months cause X1 couldn't handle CPU efficiently. I love Pro-channel modules though. The flyout quad-curve is nice.
@George: I saw your post on this chopping issue in KVR. Tried to recreate in X3 but couldn't. If you want me to check then let me know the steps otherwise wait until they release a demo. If you don't want all the plugins then consider downgrading to Studio version. It has got everything the producer has (even Melodyne) except a few Pro-channel modules and Quadcurve flyout option. I know, you know that already :-)