Upgrade to Homebuild PC

Should I stay with my AGP rig witch is: an ASUS P4S800 Mobo, a P4 @ 3.4GHz, 1.5GB of PC3200 RAM, and an Sapphire HD3850 AGP Video Card.

Or,

Should I get this PCI-E setup: an MSI Mobo(not sure what model), a Core 2 Duo E4600, 2GB for PC5400 RAM,and an HIS HD2600Pro Video Card.

If I get the PCI-E parts they will be coming from a friend and they all work as ive seen it before. I would just like to know if I would loose any performance due to the 2600Pro not being as strong as the HD3850. Please don't point out any suggested changes because I have no money to spend currently, I'd just like to know if the PCI-E rig would be better or about the same.

Edit: I mostly play games like: Crysis, COD4, COD2, NFSMW, GRAW 2 at 1024x768 res and id like to have them at med to high detail with adequate performance. I'd like to know which rig would be better for that.

Well i play games like Crysis,COD4,COD2,NFSMW,GRAW 2 and some online games but would the Core 2 Duo outperform the old P4 at a 1024x768 res on med/high details? Reason being is I average 15~20 FPS in Crysis with high details at that res

You sure because my P4 rig kept up with the Core 2 Duo rig in CoD4 at 1024x768 res with max detail

Yeah i saw that article a few min. ago attempting to find my answer on google but the thing is my CPU is already OCed its actually a 3GHz Prescott I oced to 3.4GHz. I'm just wondering if it is worth the change with the type of games I play at the details/res i run them at.