I've got two WD 80's that I RAIDed together. 160GB total, but I set my "Active Partition" on the larger drive. 😱
If I wasn't so lazy I'd go back and redo the whole thing. Wait a minute... I will... this week... sometime...
Anyway, I doubt that you even detect any speed difference (without benchmarking), by partitioning the drive up. Just make it a 10-90% or 20-80% if you load a bunch of stuff to your Windows partition.