Top vs bottom/isolated affect power supply recommendation?

[Luke M]

Does whether the power supply is top mounted (acting as an exhaust) or bottom/isolated affect the best choice of power supply?

Here's my thinking: if the power supply is isolated from system airflow, then you want the minimum fan speed (zero if possible) which is needed to cool the power supply. But if the power supply is top mounted, then the fan is useful for system cooling even if the power supply doesn't need it, and a temperature controlled fan is not necessarily optimal. If the fan stops completely, then not only is the fan going to waste, but the power supply is heating the system by allowing backwards airflow from the exhaust into the case. Perhaps a quiet constant speed fan would be better, or alternatively, a motherboard controlled fan (I haven't seen any power supplies with external fan control, though, so you'd have to modify it yourself).

[Parappaman]

If you have a decent case with a little airflow (read: a rear exhaust fan and front intakes) and don't have tons of video cards installed, either will be just fine.