Thanks for the replies.
The R300 is being used in a residence, and the main issue is streaming video (to iPads in particular). The video is sometimes choppy/cutting out in certain locations. The problem locations are ones where there are multiple walls, or a wall with some electronic equipment, in between the iPad and R300. The solution is probably to move the R300 (to a more centrally located ceiling), but that would involve running a PoE cable. So I was looking for an easier solution and was curious if a R500 would do better (a number of these have been showing up on eBay recently). Doesn't sound like it though. So I'll probably just bite the bullet and run the cable.