Re: How limited am I by the E6600?
More and more games are coming out that utilize a Quad Core CPU. As that trend continues, you will become increasingly limited by your CPU.
I also had an E6600 overclocked to 3.2Ghz coupled to an 8800 GTX (died, RMA'd, got a 9800 GTX+) and it was a fantastic system. However, my current setup with a PII Quad Core and a 5870 is far superior. It's ridiculously apparent in games like BC2 and Metro 2033 that use a Quad core CPU extensively. For games that just use a Dual Core or single core CPU, you will see a definite improvement.
I say go for it. The GTX 460 will be a significant upgrade from your current GPU, and you will see a difference in games that aren't heavily CPU limited.
AMD Phenom II X4 965 BE (RB-C3) @ 4Ghz, 1.425 Vcore, 1.25V NB VID
Thermalright Ultra 120 Extreme (w/ Scythe Gentle Typhoon 120mm fan)
Gigabyte UD3H AM3 790GX motherboard
XFX Radeon HD 5870
PNY XLR8 2x2GB CL8 DDR3 1600
G.Skill Ripjaws 2x2GB CL8 DDR3 1600
Soundblaster X-Fi Fatality Titanium
OCZ Vertex II 120GB SSD (OS drive)
Western Digital 500GB Caviar (black)
Western Digital 640GB Blue
Samsung DVD burner
Logitech MX performance mouse
Logitech G15 keyboard
Corsair HX 750-watt Modular PSU
Antec Nine Hundred case
Windows 7 Home Premium x64
ASUS MK241 24" LCD
ACER X241W 24" LCD - RIP