Fastest P3 Xeon is a 700 with 2mb cache. Fastest P2 Xeon is a 500 with 2mb cache. I'd recommend a SuperMicro or Intel board, and go with whichever you like based on the options you prefer. Going with a i840 based board is gonna cost you in memory since the RIMMs must be paired, but going with a 440GX based board you won't have much of an upgrade path and not have as many options. SuperMicro also has some of their own chipsets, but I am not sure how well they perform or how compatible they are.