Why get a card as good as the 7750 if you're not going to use it properly? OP, a mere ~$30 350-400W PSU from Antec, Corsair, Seasonic, PCP&P, or XFX would be ideal.
my statement was more supposed to imply not to ever change that resolution to 1920x1080 or possibly anti aliasing to some extent, then the cpu may or may not start to take a heavy load and hit that 100% mark which would then hurt performance. What I was trying to imply was that if your cpu is having a hard time, lower the settings if necessary.
and i whole heartedly agree on a psu change as well.