No, file size makes no difference. Again I must say this. The playback device just plays what it is loaded with. It does not "groan" or struggle, or stutter under the weight of a larger file.

The ONLY difference size makes is in regard to the amount of storage one has available, period!

I agree that a quality MP3 (and certainly well above 128) through a live P.A. is fine, I use them myself, but only for storage space restrictions.

In my case I use VBR at the highest quality level (= files of approx 6-8mb in size) and through a PA these are pretty much indistinguishable from WAV.

But the MP3 must be 256kbps or better, anyone who cannot tell the difference between a 128kbps MP3 and one of 256+ needs to have their hearing checked. The difference IS very noticeable.