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Whether this would be a benefit to your overall system performance depends on a number of factors. For example, if you choose a semi-fanless PSU such as the Corsair SF450, the top vents will help to keep the PSU cooler when its fan is off (if it's facing upwards). If the PSU fan is facing into the case then the warm air within the case will make its way into the PSU and likely activate the fan at a lower load.If you have a PSU that the fan is always running, then having the fan face downwards will indeed assist with system temps to a degree, although depending on how much clearance there is the to the CPU cooler fan you may get opposing direction airflows. Also pulling heat through the PSU will cause its fan to run at a higher rpm to compensate, so overall you may in fact end up with a louder/noisier overall system even though the system temps are slightly lower. It really depends on which components are your loudest, if your GPU is loud for example then the PSU fan noise might not matter.
Whether this would be a benefit to your overall system performance depends on a number of factors.
For example, if you choose a semi-fanless PSU such as the Corsair SF450, the top vents will help to keep the PSU cooler when its fan is off (if it's facing upwards). If the PSU fan is facing into the case then the warm air within the case will make its way into the PSU and likely activate the fan at a lower load.
If you have a PSU that the fan is always running, then having the fan face downwards will indeed assist with system temps to a degree, although depending on how much clearance there is the to the CPU cooler fan you may get opposing direction airflows.
Also pulling heat through the PSU will cause its fan to run at a higher rpm to compensate, so overall you may in fact end up with a louder/noisier overall system even though the system temps are slightly lower. It really depends on which components are your loudest, if your GPU is loud for example then the PSU fan noise might not matter.
