Huge difference between the 750 and 760. You should be looking at the 750 TI as a minimum. If money is an issue, buy used.
Also make sure that your power supply can support whatever GPU you're upgrading to.
Thanks! Looking at what's available, assuming I jump on a 770, do I go MSI or Zotac? Are they inferior to EVGA or Gigabyte in any way?
And I'm assuming that once I crack open the case, the power rating of the power supply should be easy enough to spot...
(This is what happens when I buy off-the-shelf... the deal was too good to turn down though.)