I play some of the most demanding games on a standard
SATA 2 Hard drive. A 500G and a 320G Seagate and Samsung drives. I have absolutely NO issues playing anything at all on either drive and my drives are also in dying need of a De-fragment.
You will be fine with any drive for playing games. If you want to have a fantastic read speed and have MONEY TO BURN, get 2 Velociraptors and set them up in
RAID.
This will give you bragging rights only and the normal human won't SEE A DIFFERENCE.
I have just finished Crysis and it was great.