I`ve no answer for the first part of your post, but I run 2x GeForce 6600 GT PCI-E cards and was concerned about temperature. When I contacted NVidia they responded:
"The NVIDIA GPU has been tested up to 145C so the 51 and 56 degree C temperatures are well within operating range."
Whether exactly the same is true of your GPU I can`t be certain but it does show they run extremely hot.
On the first part, have you anything else running which may be taking up resource needed by the movie?