The 36.7 GB Raptor is much noisier than the 74/150 GB Raptor. For the WD740, Western Digital redesigned the spindle to make it produce less heat and noise, and therefore be more conducive to a desktop environment. Because you have two of them, there will be a lot of noise coming from your hard drive cage when you play a game or do anything that requires a lot of reading from the drives. Idle noise isn't bad, though.
The 36.7 GBs in RAID 0 would have greater transfer rates, but because your computer has to search for the data on two different drives, your seek times will go up a small amount.
If you really want a Raptor, I would go with a single 74 GB. It's plenty fast, you'll get the same capacity, and you can buy one later for a RAID array if you want. I think once you get it, you'll be pleasantly surprised.