I refer to my rig in system specs. After building it in May 2007, oc'ing it to 3.0Ghz and upgrading from 8600GTS to 8800GT I feel the upgrade bug strike me again... For now I'm excluding graphics card upgrade because my 8800GT serves me well, and also motherboard upgrade because were I to get a new motherboard I'd prefer to save up some $$$ and get one with at least 2 pci-e slots and ddr3 which is not practical for me now at all. The piece which needs most priority in upgrading (correct me if I'm wrong) is me E4300, and I don't exclude getting Vista and investing in 2GB more RAM (I sooo want DX10 graphics!). My motherboard is the Asus P5B: - Support Intel® next generation 45nm Multi-core CPU - Intel LGA775 Platform - Intel® Quad-core CPU Ready - Intel® Core™2 Extreme / Core™2 Duo Ready - Intel® Pentium® Extreme / Pentium® D / Pentium® 4 / Celeron® D Ready - 1066/800/ 533 MHz - Dual-channel DDR2 800/667/533 - 1x PCI Express x16 - 6x SATA 3Gb/s - RTL8111B PCI-E Gb LAN - 8-channel HD Audio - AI NOS™ / AI Gear / AI Nap What I'd like to know is what is the best quad core I can put in this thing. Does the 1066 limitation mean that I cannot put in a processor which runs at 1333? Does the 800 limitation mean that I cannot put in RAM which runs at 1066? I want to get the best quad core possible, with good cache and with a high multiplier because I want to oc it. My budget... I'm looking to spend around less than USD500 though I could stretch that a bit. So... what would be the best quad core and best RAM I could opt for right now?