With regard to this PSU support thing, I installed mine slightly differently - the easiest way, I think, to explain how is a 90° anti-clockwise rotation from how garsands has shown how his is installed - such that the triangular bit is acting as a shelf. My photo on pg 5 just about shows what I mean.
As far as flat cables go, though they may help slightly, flat cables aren't the saviour - the issue, at least what I'm seeing (HX750), is more to do with the connectors on them as opposed to a huge mass of wire. I intend to take some connectors off the cables to alleviate the issue of space behind the motherboard tray.
Overall though, I'm chuffed to bits with it.