should i install windows on 2 5400 x2 raid 0 or single 7200 rpm?
(as in speed)
I would probably just go with the 7200rpm drive for OS because of the added reliability, and perhaps use the other 2 for media/games etc.
You should also keep in mind how sizes work with RAID. the overall size of the config is the size of the smallest drive times the amount of drives in the config. For instance, if you have one 250GB drive and one 500GB drive, your overall capacity will only be 500GB (250GBx2), in cases like this the only reason to have RAID is for added performance. Maybe you already knew that.
i got 2 160 gb, so i just thought about putting in raid 0 and reinstall windows