Here we go again to another upgrade!!!!

Hi guys, I need your help, because I can't make up my mind!I must say that this PC is to run only FS!!!Hi have the following specs:Asus MBO P4E800 DELUXE socket 478 P4 at 2.66MhzNvidia GF6800 Ultra AGP 256Mb1GB Kingstone RAMHDD 120Gb Seagate ATA133What I decided already to change:Motherboard and CPU (because I can't get a 478 Skt CPU anymore)Hard Drive for a SATA II dual drive runing RAID config.What I didn't decided yet:If it's worth to change my graphics card I bought at the beginnig of the yearSo on motherboard and CPU:1. Is it worth consider the move to dual core? AMD of Intel?2. Will be more cost effective to consider P4 3.2 single core, and mantained AGP instead move to PCIe and so change the graphics card too, wich will represent far more expensive? Is will improve the cost/improvement ratio so heavilly?My point here is:Will I improve so much the FS experience changing almost all the system? Will I improve the performance in great shape only changing the MB CPU and HDD, (but single core and AGP, and so far more cheapper) without changing the Graphics card and save half or more of the money?Any help to decide, pretty much appretiate.Cheers to all,Miguel