Has anyone noticed a 1.6 fold speed difference in forcite optimizations between windows (XP) and RHEL 5.3 with windows being faster?

I have a forcite optimization that takes 17 minutes on a 3 year old laptop running windows XP and 28 minutes on a dual core opteron machine (Sun Ultra 20M, 1 1/2 years old) with 4gb of memory running RHEL 5.3. I find this very surprising...