I've had very good experience with the R300, 320, 500 and 550 unleashed. The most I've ever needed was 15 at one location. I have a client who has some R550s and wants to replace their other APs (other brand) with R750s. Do they get POE over the 2.5gbps connector ? I've never worked with anything over 1gps poe.
Also they will probably have about 20 APs in total between the R750's and R550's - any problem with the unleashed running off of one of these as the master in an unleashed config? I heard they used to recommend a director or something once you got to a certain number but also heard that restriction was going away with the new units.