If your dead set on 243 which is a fine round very versital you will be shooting alot less then 800 yrds. Best inside of 300, IMO. If your willing to change the calibar you can open up all kinds of possibilities but with them comes skill and practice. Im assuming your newer to hunting with your 800m comment so Id like to give a bit of advise. You dont buy a 16 yr old a Corvett for there first car cause they dont have the experince to handle what that car can do. Same with guns You can kill deer all day with a 243 inside 300 yrds and be a great hunter. You dont need to start your hunting experince with 1000$ invested in long range shooting equipemnt when your learning the ropes.
Good Luck Niccum