It should be ok, but the way to really know is to test the temp of the basking spot to make sure it's ok. Some factors are your ambient room temp and how far you raise the powersun off of the cage roof.
As far as going to one bulb, I use a powersun, but still use flourescents to evenly light the cage and give the plants the light they need. Also, I've read that chams really like it bright, so if there were dark spots in the cage, they wouldn't use them. Some people hang strip lights on the side of the cage.