1. I really do not see much if any temperature differences.
2. Bootcamp will be faster because you will not be running osx on top of it as you would with a virtual machine.
3. From my personal experience I had more battery life issues in bootcamp than virtual.
One more thing I like to add, the nice thing about a virtual machine is the ability to access your osx applications on the fly when needed, instead of switching back and forth between bootcamp and rebooting into osx.