Well you need to make sure it does stay under 12ft lbs! If you buy the correct ram for the rifle, all should be fine.
Max range all depends on your ability. If you can hit the kill-zone consistently then you'll have no issues dropping any airgun quarry out to 45 yards. It all comes down to how confident you feel with your kit mate, but make sure you put the range time in, and practice at different distances too until you're getting sub inch groups consistently.