ORIGINAL: one on one
50 to 100yds, but no more. good luck
Bad advice... taking shots at 50+ yards is getting dicey, esp. on moving deer, and is an invitation to wounded & unrecovered deer... shooting anywhere near 100 at unwounded deer, is just plain wrong, IMHO. You're much more likely to would than to kill.
Most of my deer have been with buckshot... it is tempting to take longer shots than you should. Todd1700 has it about right.