That should be okay since graphics boards only reach a temperature fresh-hold about 100 degrees C. They can run hotter than CPU's fine, and since yours is a heat sink only board, its definitely fine, as I wouldn't expect it to run cool.
My 6800 on the other hand on this old machine can sometimes reach 116 which causes a throttle back, slowing the card down, and slowing the game down as a result.
Its then that you have to worry and consider things aren't right
The only thing I can advise is check wires are clear, and that you have sufficient cooling sending air in and out in your case. Otherwise, air can't escape, and so, a board with no fan will just get hotter as it can't push air out itself.