The 750 Ti is only very slightly cheaper than the 1050 Ti in most regions, while the 1050 Ti can be 70 % more powerful(depending on the games in question). If you can return the 750 Ti, I would do so.
And the 6300 is multiplier locked, so you would have to increase the base clock rate, and unless you have a decent aftermarket cooler, you would not be able to get OC gains worth the time for that CPU. And if you don't already have that cooler, I would not spend money on buying one for that system.