Well a single 690 is significantly better than a single 680, and neither require a SLI motherboard. Then again, I wouldn't buy either one considering the 700 series is out and a 770 is literally the same thing as a 680 but usually cheaper.
A couple HDDs and an SSD hardly take any wattage. If you are limited by connectors then that's one thing, but other than that amount of drives or fans really is irrelevant.
To give you you a broad answer. A 750w PSU like this one would run either a single 690, single 680, two 680s, or two 770s.
Corsair 750W HX 80PLUS Gold Modular PSU | Ebuyer.com
The GTA remark was from another member to me. I'm the one doubting they will release GTAV for PC anytime soon after the console release.