depends of what readings of uvb you get ! for example i go for the 10.0 cose the mesh i used is thicker ! so the 5.0 for me was to low !
i'd say 10.0 is ok too depending of the mesh and how much it blocks the uvb,the height where you put the bulb,how large is the cage etc...
personally i find 10.0 better, and i know lots of pple who use 10.0 and nothing wrong happened!