Just noticed that for £5 more i could get the 650w and £14 more a modular 650w XFX. Would you recommend stepping up. Is the modular cabling worth it?
I would bump up to 650w for £5 more. This will be enough for a dual vid card set up later if you decide. If not, there is no waste getting extra wattage these days with the new Certified units.
Modular is more worth it with a top mounted PSU as it is a bit harder to tuck cables away. With a bottom mount, you can just let the extras rest on the bottom of the case and tuck the excess under the hard drive bay.
One other trick is for the 8 pin motherboard 12v CPU power cable. Install this before the video card and run it up the back of the motherboard. When you install the video card, there should be a notch cut out between the back card edge and the metal plate that fits the back case slot. The 8 pin cable will rest nicely in this notch keeping it out of the way of things.
Similarly, the 24 pin ATX power cable can be run along the front edge of the motherboard. Any excess can be tucked under the drive bays. Then hook up the hard drive/DVD power cables and let them follow the same path. I would plug in the PCIe cable last and route it accordingly.