I have a Core Duo Blackbook, which gets much hotter than your model and is slower. I've converted videos using Visual Hub for an entire 13 hours straight several days a week since last year and mine is still performing with no problems. i just ramp up the fans with smcfancontrol (just as a habit while encoding) and let it go. Mine reaches 90-95 degrees celsius when converting using the H.264 setting.
Long story short, I think yours will be fine if it doesn't have any hidden issues already present 😎
As a side note, does anyone know what factors determine the speed of conversions like this? Just trying to decide between a 2.8 MBP and the 2.4 MB.