Bub
Here's my experience with X2 ...
I'm running an Intel i5 Quad core with 4GB RAM.
M-Audio Fast Track Ultra
Windows 7 x64
Sonar X2 Producer x64
I can run an 18 audio track project with a few modules active in the Pro Channel on each track ... then my system dies and I have to start freezing tracks, which I usually only have to do with things like Session Drummer 3 and Dim Pro. Seems to me, X1 allowed me to run more things before I had to freeze.
So my advice, get the biggest, baddest, fastest DAW you can afford, from folks such as Studio Cat or others. I always build my own, but I'm not going to any more. I want someone I can go back to when things don't work ... and it inevitably happens. I've only had one DAW over the years that didn't give me a lick of trouble.
Sounds a little sticky, IMO. Look at my specs - 32 bit, dual core with 3 Gb RAM - in PE 8.5 I can run 15 audio tracks + 15 MIDI tracks (say Kontakt with 4 outs+Addictive Drums with 3 outs+ManyBass + some lighter soft synths) + at least a dozen audio FX (EQs, compressors, choruses) quite fluently with CPU usage below 50%. Above those figures I freeze Kontakt.
When I add, say, Vocal Strip and Perfect Space on top of that, I need to freeze more.
I do realise, though, that Pro Channel is surely quite a heavy tool on the CPU. But your system is so much faster than mine.