I'll have to give this a look... Bare in mind that if these scores are accurate and you score say... 410, you wouldn't' want to use a 420W PSU. The closer and closer you get a system to its PSU's max load the better chance you have of frying something. Also when ran that close to its maximum its going to put off a lot of heat raising your systems temperature. I always shoot for at least 20% headroom, and if you plan to expand the system (More hdds or maybe even a new video card 30-40%!!
, I also shoot for supplies that have 80%+ efficiency, cool little guesstimating site though
karz - I would rely on the TR stuff first off, they provide real-world testing on devices in person. The draw from the wall is not what your system is actually using either, this depends on the efficiency of the PSU your using, im sure TR includes this in their reviews and guides when talking about PS units.. they are quite thorough. As for the 12v Rails....... On many top end modular supplies they will have each plug port listed for which 12v rail it runs off of. In addition a few of them will be listed as having 3 or 4 12v rails and 1 of them will be reserved for the CPU plugs, and the others for whatever you plug it into. Hope this helps!