I own that CPU. It can hit 4.2GHz on stock cooler with zero issues and on first attempt in most cases. For more, aftermarket coolers are recommended. I was able to get to 4.5GHz on first attempt on Arctic Freezer 13 cooler, and did not even try to go further. Running at just 1.23V, 24/7 prime stable.
This CPU won't bottleneck anything when overclocked, so get any card you like. I own R9 280X, runs like a champ. You can certainly go much further than 750Ti. Just don't go SLI/Crossfire.
Make sure your PSU is up to the task as well.