I'm planning to build from a barebones system with a motherboard that has a 400/533/800 Mhz FSB for Socket 478 CPUs. I have two 256MB ddr PC2100 memory chips I'd prefer to use, and I want to put in the fastest CPU that makes sense. I assume I could use any Socket 478 800Mhz P4, but I don't know how the slower DDR SDRAM will affect performance. Is it a waste to get an 800Mhz CPU (I wanted the hyperthreading) if I use the PC2100 chips? Would a 533MHz CPU also waste performance potential with the PC2100 memory? I want my optimal mix of CPU and memory, but since I'm building from surplus hardware I already own and only need to buy the CPU, I'm trying to make that my only new investment without paying for potential CPU performance I'll never see with the PC2100 "bottleneck". Thanks much.