Yes, SSDs are fantastic at reducing game loading speeds. It's actually annoying sometimes that I can't read the "tips" that flash on the loading screens : P
All joking aside, I would go ahead and pick up a SATA III SSD instead of a SATA II, even if your current motherboard only supports SATA II. Your drive will most likely make the move to the next system, and there is typically very little difference between prices and there will be no harm in using the SATA III SSD on a SATA II port.
But hey, if you find an amazing deal, but whatever you want : P