What kind of performance with high powered machines?

I am thinking about upgrading my machine, but am wondering if it is really worth it. My current specs are a Dell P4 1.9 (old socket), 764 megs of RAM ( or whatever that mutliple is ), TI 4200, Santa Cruz sound card. I have been eying some refurbished Dells with the 2.8 to 3 gig chips as well as their new gaming machine with the newest Intel 3.0 gig chip with Hyper threading etc. I fly: PIC 767; DF 737; IK DC-9, Flight 1 Commander, Flight 1 Cheyanne; Briefing Time. I run in multiple monitors with the second one running off an old Matrox card - only static panel pop-ups on the second monitor. I use FSNavigator, and sometimes FS Flightmax. I have a lot of AI, though set the settings for 50%.Here's my question:I have a lot of trouble flying in real weather conditions because the clouds bring my system to a grinding halt. I'll be flying along at 22 fps (locked at this rate) at 20,000 feet in my DF 737 - but when I hit the clouds, I'm down to low double digits, and into single digits close to the ground. If a new machine gives me a 60% increase in cpu firepower, does that translate into roughly a 60% increase in frames (ie. going from 6 to 9?) - or is there a greater leap for reasons I wouldn't understand.I have the same question about busy airports. If I get 10 fps at a busy airport with 50% AI, will I get 15 after the upgrade?I guess I'm wondering if I should wait even longer. I'm not convinced that even 3gigs is enough to drive msfs with all the bells and whistles.ThanksColin