RE: Mule Deer Gun
 

No need for a magum or the cost of magnum ammo for deer in my opinion. There are plenty of smaller caliber cartridges that provide plenty of velocity/power for deerat longer ranges than most hunters couldever accuratly shoot.Having an accurate MOA rifle is far more critical than power (especially)for deer.
I assume you are in open country, the 270 win is at the top of my list and provides 3000+ fps factory loads.Ammo is 30% less than any of the magnum ammo when comparable bullets are used. The short action 243 and 7mm08 are great choices if alight weight rifle is important.

RE: Mule Deer Gun
 

It makes no difference what you use as long as it's a 270 or 280 or 6.5x55 or 308. There are many other good ones but over many years I have dropped about 350 Mule deer with those four calibers. As a kid I killed quite a few them with a 22 LR.