I had a small powder blue ($18 at a crappy fish store!) that was in my 125 reef for 5 or 6 months until it just disappeared (body was never found, I attribute that to scavengers in the tank being pretty darn effective). I also had a large 8"+ that I bought for $5 because it had been left out on the runway at O'Hare airport for 5 or 6 hours in the winter time and was not doing well. It ended up dying the same night I bought it, but I don't blame myself for that at all. It was lucky to survive as long as it did in my opinion after what it went through.
The one that lived for a while, it did very well in my reef, but it was very small. I don't think a reef is an appropriate place for a powder blue, the same as for a number of other tangs, like nasos, vlamingi, unicorn, achilles, and any that are free swimmers. Our reefs are more geared towards fish that will swim in and out of the reef itself, not towards those that swim around the reef. Powder blues often swim in large schools and will cruise in the open wate above and around the reef, stopping here and there to pick at stuff, but they're not like the yellow tangs that will hover over a certain spot and pick at it for hours and dart in and out of hiding places in the reef.