I am building a new pc with the intention of OCing the cpu. I am wondering what the best cooler at ideally no more than £50 to get for this build would be - I would prefer to go on air so if 4.2 wasn't possible on air what do you think the best I could hope for is without my computer sounding like it's about to take off in to the sky?
Secondly I'm thinking of going for a 750w power supply for this build and I am wondering if that is what to go for or if I should go smaller.
Your best bet is a 750w power supply. Overkill would be 850w, and a 600w will be pushing it, however it can be done. I have Almost the same setup with CPU/GPU and I am OC'ing my CPU to 4.2 and the system is stable. 750w will be great and future proof.
On the PSU, 750W-850W would work well. I would choose a Seasonic X-series or Platinum series. Second brand would be a Corsair RM, HX, AX or AXi. Go bigger for the power supply since you are overclocking.