RE: What to upgrade to?
The Intel P4 2.53 GB is going for about $200 (w/fan). There are a bunch of good motherboards for it, but I have had excellent results with Gigabyte. I would probably go for a model that uses DDR memory rather than the more expensive RDRAM. The best graphics board around is the ATI 9700. ATI is bringing out new models, so prices on the 9700 are becoming more reasonable.
P4 2.53 ABIT TI4600
512 RDRAM 1066
Windows XP Home w/SP1
I7 3770K OC 4.5ghz ASUS Sabertooth Z77, GTX 660 TI 2gb, 8gb RAM, Win 7 Home 64 bit, CH yoke, Pedals and Quadrant