Okay let me try and clear some stuff up for you OP. People really over react when their CPU isn't fast enough for their GPU (bottlenecking), but the truth is something is always going to be the bottle neck in your system and what component is holding you back will vary depending on what game your playing.
Now a Core 2 will cause a bottleneck with a 760 on games that use the CPU more. On most games your not going to see hardly any reduction of your GPU's performance, only on the most CPU intensive games.
A 7750 is a good card if you on a budget, if you have money to spend, spending more will give you much better results. Right now a 760 is the best card in the $200-$300 dollar range, partly because it's brand new.
Get a 760, your Core 2 is going to handle if fine in most cases, when you want to upgrade your CPU you'll want to step up to the 1150 platform anyway, meaning a new board as well.