I have a custom built .264 win mag and love it especially for deer sized game. I hunt mule deer at extended range and it has worked well for me for the last two years. The last mule deer I shot was at 322 yards and dropped it in its tracks.
I have also shot a coyote at 435 yards. I took the gun elk hunting last year as well and would not hesitate shooting an elk within 500 yards. I am only able to shoot a spike in my area unless you are drawn for a special permit, but I have seen many elk shot with lesser calibers.