The ideal method is the one used by Antec in their P193 / P183 series.
As you can see here, the PSU area is completely isolated from the rest of the case
http://www.newegg.com/Product/ImageGallery.aspx?CurImag...
They also have the intake and exhaust on PSU as a straight thru run thru the PSU.....no 90 degree angle resulting in less turbulence, better cooling and less noise.
silentpcreview commented on the "integrated design" of these cases (1200, DF-85, P193, P183) and the CP series PSU's in their review of the CP-850 but I can't bring it up as their site is down atm. Here's the cached version
http://74.6.238.254/search/srpcache?ei=UTF-8&p=silentpc...
Quote:
A serious consideration is that in each of the three [now four] compatible Antec cases, the CP-850 mounts on the bottom, and the intake for the PSU is quite separate from the rest of the system. In the P193 and P183, the PSU is in an entirely separate thermal chamber, and in the model 1200 [and DF-85], a direct path can be maintained to the directly opposite, wide-open front vent. This means that our extreme hot box test conditions never apply to the CP-850; in other words, SPCR's test environment is unrealistically hot for the CP-850. Our atypical spot check with a room ambient thermal test showed the CP-850 would reach only 24 dBA@1m at 700W load in a 27°C working environment. This is ridiculously quiet for such high power output.
The above is an obviously unfair advantage for the CP-850... but what of it? Antec has used an integrated systems approach for its CP-850 and its best cases, and if that approach is an advantage over all other case/PSU combinations, then, all the more power to Antec! It's not uncommon for enthusiasts to frequently replace the motherboard and components that mount onto it — such as CPU, RAM and video card — while the case and PSU are retained. There would be ample reason to take that approach with the CP-850 and one of the compatible Antec cases.