I know this thread will soon be a month old but I had to reply to this, the reason the software raid in windows benches better than the hardware raid on the motherboard that person mentioned is because unless the person giving numbers was running a very high spec server board in his PC (unlikely) then it wasn't hardware raid.
Just because you have an Nforce or Intel motherboard with raid in the bios doesn't mean it has hardware raid its just software raid and its still handled by the CPU, the difference is that with motherboard based SW raid the raid is handled at a level above Windows (hence why the partitions are bootable/etc) so windows just sees a disc and with Windows SW raid its all handled by Windows.
The increased performance is probably due to windows being in charge of the file copy and the raid whereas with MB based SW raid windows is copying to what it sees as one physical drive and the motherboard is handling the raid at the same time using the same CPU and the windows raid method is more efficient in this situation.
A hardware raid controller (a proper £100+ add in card) will always outperform software raid if using the same discs and raid mode as it has a dedicated cpu/memory.
