Truth be told dude you are better off getting the later model heatsinks, they were better at cooling the system down and with good thermal paste + the later model heatsinks they weren't that hot. I might have a few here, PM me on skype if you want me to send you them?
From what I can remember also it wasn't really a temp related issue that the 360 had. More than anything it was poor solder joints on the GPU that cracked and stopped the system from working, so reducing voltage might not really be needed. At the end of the day most laptops run 80c+ daily without much issue.