You may wish to PRINT THIS FOR FUTURE REFERENCE.
You are asking if you can overclock your i5-750 even higher?
Not much likely. Why do you wish to?
1) it really won't matter for GAMES.
2) you'll be adding heat, thus noise, and increasing the possibility of killing your CPU.
Not only do I not recommend overclocking further, I recommend keeping your present overclock to no more han 3.8GHz.
So you STILL want to overclock?
1) The better the CPU cooler, the better the overclock (up to a point).
2) Frequency is increased until the CPU stress test or booting causes a CRASH
3) then the CPU VOLTAGE is slowly increased until things seem stable
4) then the CPU frequency is dropped down slighty (200MHz or so) to help with stability
5) double check that you did NOT overclock your RAM (usually you can just adjust the RAM's MULTIPLIER value, for example:
200MHz base clock x8 = 1600MHz
(if you overclocked the CPU and has a x12 base clock and 200MHz then your computer would try running RAM at 2400MHz and the RAM would cause your crash, not your CPU necessarily).
SUMMARY:
I don't recommend you overclock above 3.8GHz. There's little to no advantage to any games and the heat/noise level rises.