it gives you plenty of headroom for later expansion.
Yes, its best not to skimp on your power supply! But would they really need a 750 for just one graphics card? For two maybe that much.. But with the specs I wouldn't think more than a 600W would really be needed. 500W would work but would be bare minimum and would need to be replaced if they decided to crossfire or something.
Need? Not right now. I don't need any more than a good 400 Watt PSU, but I have the Silencer Mk II 750 Watt. If by some miracle I were able to upgrade from my single GPU to a pair of GTX-670's for SLI next month, or if the OP adds another 7850 next year for Crossfire, there's no need to worry about getting a new PSU to handle the added power requirement Spend the extra $30-50 now & save $100 later on down the line.
Buy the minimum you need & in the long run, you'll spend more money overall.
I started using 550 Watt PSU's a decade ago... by following this method/philosophy, I average one new PSU for every 3 re-builds, following a 3 year re-build cycle. The PSU that powered my AMD Athlon XP 2500+ & Athlon X2 4400+ rigs, was the PSU I used when I built my current rig. I only upgraded it because I was looking at the possiblity of Bulldozer + SLI. Though with things happening IRL the way they are, & Bulldozer being such a steaming pile... that's no longer on the horizon. Still, this PSU should last me for at least the next decade. Just wish I could say the same about GPU's & CPU Heat Sinks...