Our experience w/RB532 is that it has no problem running 2 SRx radios. If you do the math on the power consumption the watts are available to run the cards.
According MT specs, 14 watts are available on the RB532 3.3v rail w/ 3 watts consumed by RB532, leaving 11 watts for running cards. 1.3A to run SR2 at full power=4.3W, meaning that 2 cards will squeeze into the supply leaving a little less than 2.5W to spare.
Those numbers assume the SR2 is running at 24Mbps or less. Once the connection hits 36Mbps the consumption drops to 2.6W and drops further yet as the rate increases, meaning the power consumption is by then not even close to hitting the PS limit.
SR5 uses 4.7 watts full up, so PS head room is commensurately less at lower rates on 5Ghz but again the power consumption falls as the bit rate goes up.
If you are running 24Mbps or less you can always dial back the cards a wee bit if you're concerned about running the PS at a little over 80% capacity.