Your 970 and i5 should be good enough for 60hz at 1080p most of the time. If you are playing at higher resolutions you may get lower framerates (or much lower at 4K resolution).

Computer overheating and freezing should not happen at all unless something is seriously wrong. I would find out exactly what components are overheating by using Open Hardware Monitor software.

If CPU is overheating, the heatsink was probably put on wrong on the i5. This is very dangerous if this is overheating, get someone who knows what he is doing install the heatsink on the CPU. and FYI, if you try to use a CPU without a heatsink it could melt.

If GPU is overheating, you probably have incorrect overclocking settings and should set it back to default overclocking, or even move it back to OEM voltage and core clock speed. If you tried to reseat the heatsink and aren't sure you did it right, get someone who knows what he is doing to install it again.

If PSU is rated at less than 400W or it is failing, you might be pulling more electricity than it can supply properly.

If the above aren't the issues and nothing is overheating, I'd do a memtest86 to see if a RAM stick is going bad, and disable windows AERO.