Looking at the Thinkwiki page for the R40 [1] it looks like they come in Celeron, Pentium 4 and Pentium M models. You’d want the 1.7Ghz version of the Pentium M for the best speed I’d think. There’s some talk of changing the motherboard out on an R40 here [2] and there seem to be plenty of motherboards on ebay for cheap.