Can i upgrade to PCI 3.0 with GA-A75-D3H motherboard

That will work fine, especially if you are only spending that much. You could look at the 7770, 650ti, and if you are ok with spending about $180-190, you can get a 7850. It is worth the price for the upgrade though.

I agree. As long as you play at 1680x1050 or lower, the HD 7770 or 650 Ti are acceptable and in you price range.
But for 1080p gaming, you will need to spend a little extra for an HD 7850 or GTX 660. But I'm pretty sure your CPU won't be able to handle them so you will not be able to benefit from all the performance these video card have to offer. What CPU do you have ? I based my comment on your socket.

PS. Your motherboard is PCIe 2.0 not 3.0, but it doesn't matter. There is no performance difference.