as unksol says, it is more than big enough wattage-wise. If you are only going to be using one 660 Ti GPU, then you could probably go as low as a 450 Watt PSU, but since you state you may be overclocking in the future, I would get at least a 500-550 Watt PSU. However, if you are looking to SLI in the future and overclocking, then the 750 Watt is a good choice.
Yeah, must admit I'm a bit of a sucker for room for expansion. Thanks for the answers!