Well I tried the PSU (a Jeantech 'Arctic' 600w Modular cable thingy by the way) using the info above, in an old DELL I have. But it won't boot using the PSU I've been asking about. If it's because of the P4 cable off of 'half the P8(?) cable (as above - I don't know).
After doing some more reading about this PSU I think I may just give up on it...
Every review or comments about Jeantech power supplies are not very good and don't fill me with confidence so I think I'll just play it safe and not risk using it.
The reason I did ask in the first place is that it 'looks' a nice PSU with modular power cables (which I believe can aid cooling) and also a higher output in watts (600w) than any of the PSU's in my other PC's.
I wanted to have all the best parts in 1 PC but the best PC I have works, so maybe I should leave it be...
Still - thanks for the advice, as always it is much appreciated.
Well after finding this, I'm now unsure again whether to keep trying to get it working...