I'd like to be on the safe side, could you (or anyone else) recommend a 600w/650w psu please. Thanks in advance to anyone that replies
I have already suggested three power supply's that will be great for your system.
Like I have already said, (as well as two others: hunter315 & dudewitbow) a 550w will be more than sufficient.
You only need to start thinking about a 650w if you have two 7850s in crossfire.