I contacted ProProducts when I ordered mine and told them what my cage sizes were and the temps I needed. They suggested my best choice and drop shipped them to my cage builder who then installed them and sent the completed product to me.
None of my cages are a T8. The pic with the black rimmed rhp came in my GTP cage I ordered from PVC Cages. The white rimmed rhp is a ProProducts panel ordered straight from them.
You should get good use from the T8. Those are nice cages.
This is from the ProProducts site and gives you the insight of what all goes into selecting the correct panel. I highly suggest calling them and speaking to them about just what you need. Its a science and they know their stuff. Very friendly and helpful when I called and shipped my order out quick.
"There are many factors that can affect which size Pro Heat™ Radiant Panels is correct for a particular application. In order to determine the correct panel we need to know the following information:
•The size of the cage (L,W,H)
•What the cage is made out of
•How many vents are installed and where in the cage
•What type of animal is being kept
•What the ambient and low temperatures are in the room where the cage is being kept.
•Is the cage being kept in a room with a concrete floor or in a basement."
http://pro-products.com/pro-heat/