I've never been at 4.5, however I honestly do not think one would notice any difference unless you have FPS running (perfoverlay.drawfps 1) though I think this would depend on your GPU bottleneck - someone more knowledgeable may be able to better answer...
I have a custom loop:
I should note that I am only able to get that clock speed with a low temp due to my luck with the chip I bought.