Man, sata 2 means nothing, the parameters for hd performance are in this order: raid, rpm, cache.
For primary only use raptors or raid 0's, because otherwise it woul have no sense.
Now the chice depends on youre cash, the best would be a 150gb raptor(yes they improved performance and not only size) or a 74, get a ,,normal,, disk as youre primary only if its not for gaming or a server.
Get the best you can afford and latter just put in aniother in raid 0.
Dont know about heat and noise of raptors, but i dont think it should be a proablam unless its a home-theater pc or you live in a desert region 8O !
What about 2 80GB SATAII 8MB 7200 on RAID0 compaired to a raptor performance wise?
For got sakes man. Google.com it. Your performance is within single digit mbs! Until the pipes are open up SATAII mean nothing, it almost referrs only to larger disks and had does not contain any improvient over sata150. The same as ata133 was no improvement over ata100.