I would change the PSU. I always shudder when i see Cooler master xtreme
*brrrr* , brings back memories of when they lied on the labels of the PSU's output. If you want an affordable PSU with good quality, this would be good:
XFX 550W: http://uk.pcpartpicker.com/part/xfx-power-supply-p1550sxxb9
The GTX 760 is around 45% faster than the GTX 650ti, so you will notice a difference, yes, even more so if overclocked.