As noted it won't make a huge difference with in-game experience but it dramatically speeds up computer start-up and load times so much so that once you've had an SSD you won't ever want to go back. Depending on how avid a gamer you are you would need at a least a 480-500 GB drive. I run a 480 GB Sandisk Extreme II as my primary boot SSD which is very fast and I have a secondary 960 GB Crucial SSD for storing my games. You don't need to worry about RAID arrays - that is for folks who need to move huge amounts of data quickly for example in video rendering/processing applications. An SSD installed normally will be more than fast enough. Keep your HDD's for storage of non-speed-critical stuff.