Move to PCI or stick with AGP ?

I am having a lot of trouble deciding what to do. This is my current PC spec.

2.6C P4 800 FSB Northwood
Intel 865GBF mobo
Kingston 512 MB DDR 333 (PC2700)
2 x 80 Gb Seagate Barracuda 7200 HD
ASUS GeForce 6800 128 MB (unlocked to 16x6)

I basically want a new 3d card and to overclock my proc to about 3.0 on stock HSF. I dont want to throw away my old processor as i want to wait for the new DX 10 cards and Conroe/AM 2.

There is ONLY one mobo which supports PCI vga cards as well as my Socket 478 proc.the ASUS P4GD1 http://www.asus.com/products4.aspx [...] odelmenu=1

Can you guys please tell me what to do ?

Should i buy this mobo and a 7900 GT ?(will this mobo let me OC the proc?)

OR

keep this setup and go for a 7800 GS ?

OR

upgrade to new proc and new mobo and new vga ? (really cant afford to)

i'd be really thankful for your expert opinions.