With the 100 grain bullets, you can take almost any deer that walks, Raver. I respect Art's opinions, but I disagree that you need to hold off only for neck shots with the .243. That's more of a .223 statement, to me!
Remember that the .243 is basically a .308 necked down to 6mm, and consider the resulting power. Not bad. DON'T use the piddlin' 85 grain loadings-- they're varminter bullets, not well enough constructed. Although the .243 is what I would call the MINIMUM for a deer cartridge, I would say it is certainly adequate for all mule deer, at reasonable ranges.
We often inflate the size of mule deer in our heads to the size of monsters. In fact, the average mulie weight is only a very few pounds (10?) more than the average white tailed deer. Would you be so concerned about the power of the .243 for white tail?