I shoot out on the prairie alot and we shoot long range every weekend.... an 06 would not be my first choice for the task. A 500 yd shot is a pretty good poke for a good shooter shooting a good rifle using handloaded ammo. Hunting game animals and planning on shooting that distance immediately seperates out the 06 for me. Given your list of animals I'd go with the .300 Win mag because I know what they can do at 500 yds and it handles heavier bullets much better than the 06. The cost to handload one round of .300 Win mag vs. the cost to handload one round of 30-06 is very small....not enough to concern ones self with. Anything bigger kicks the snot out of you just enough to never get comfortableto shoot well. JMO
Fixed power scopes are for targets and prairie dogs not hunting rifles.