How does Sonar X3 work with a CPU Intel Core 2Quad 2.4 GHz, anyone had any experiences yet? thanks

Fine - I've got a Q6600 (quad core, 2.4GHZ, although overclocked to 3GHz), 4GB RAM, Windows 7 and no problems with it.

yup, Q6600 here. still on a intel DP35DP mobo win 7 and win xp drives.  Sonar 8.5, X1, X2, X3. I mostly do audio, so it works for me

Q9300 (2.5GHz) w/ 8GB RAM on an Asus P5N MB, Win7 x64 and a Scarlett 18i6.   SONAR X3c runs great with this combo.

Depends on what you want to do. I used that system until April of this year or so, so really with X1 and X2. It was very workable but not very "snappy" once I had more than a few softsynths running. I have to say I was very happy to upgrade to my newer system. 
If you can go 64 bit and have more than 4GB RAM it will definitely help, especially with larger projects.

wery well!...look at my specs...

My setup (below) works fine...even with lots of softsynths and effects at 128 sample buffer

One of my computers has a Q9300 2.5 GHz and 8GB and I used to work with Sonar 7-X3 with Edirol FA-66. I recently changed to an i7 3770k with 32 GB. The new system manages it much better as expected, but the Q9300 is good anyway. The approximate performance of the new i7 3770k over the Q9300 is just about 4 times faster but $1000 versus $4500 in terms of cost.
Enjoy making music!!!
CCR.

I have to admit I only have 8GB RAM and one SSD (I reused my case and my old HDDs for my audio recordings) but I built a pretty spiffy 3770 based system for like 800 bucks about six months ago. SSD, mobo, CPU, RAM, videocard (which was 250 on its own). Sincerely hope you don't spend more than 1500 even with a new case, more RAM and a few HDDs.