Not exactly voltage,
It is more likely sensitive to current, there should be enough "juice", specially during CPU and wireless cards power consumption spikes. But power source has definitely influence on RB performance, some people trying bandwidth test with RB hooked on batteries in order to supply as much current as possible to gain maximum results.
In my cases 48V source with PoE does that job fine, becouse with that voltage you need times less current to achieve the same result. A lenght of UTP wires is important too-they do have own resistance, longer wires "consume" some amount of current themselves because of their internal resistance.
You can even have a faulty RB532, there is an power issue (wrong onboard capacitors value or such), it appears when RB532 is fully loaded with cards and installed RB502 doughterboard fully loaded with cards, then is RB532 or RB532A unable to boot. In this case you should contact your RB vendor to replace board, but this is unlikely, because it affects only a few boards.
Which problem with performance you have ? Please be more specific.