my cousin hunts in the davis mountains in west TX, has for the last 30 yrs, ranges are long(250 to 300 yards is fairly common) and mule deer are pretty tough, tougher than your std whitetail anyway, he uses a .300 H&H with a big scope FWIW, but he told me the most common calibre folks he knows use is the .243, which suprised me, followed by .270's with a few .280's and .30-'06's thrown in, i can see all but the .243 go figure wouldnt be my choice.
as far as # of deer i have shot i couldnt begin to remember lol, certainly in the 100's, really dont hunt deer much nowadays, i enjoy going with my buds(actually its my place), enjoying the great american outdoors and such, & would like to maybe get a really big one someday, but i rarely hunt deer anymore, but i was plenty boodthirsty when i was younger, and was lucky enough to always have access to places to deer hunt,
i do enjoy hog hunting nowadays, i consider killing them a public service lol.