[rules-users] Unexpected performance difference on different hardware

My dev box runs Windows XP with an oldish intel core 2. It processes my rules in 13s, with a peak memory usage of about 600MB. When I run the exact same code on my 64bit linux server with a quad 2.40Ghz Xeon, it takes 22s and uses a peak of 1.5Gb memory. What on earth is going on here? I would expect it to run faster on the server and for the memory usage to be similar. Cheers, Tim