I had a friend that had an original XP-100 in 221 Remington. With the addition of a good scope and a sling that looped around the back of the neck we could hit the target at 200 yds. all day long from a sitting position at the shooting bench. The most accurate pistol I ever saw.
I have a 2X8 Pistol Scope on my XP-100 and a 2.5x8 on my Thompson Contender. (Actually have three of those, one on my .221 Fireball Barrel, one on my .22 Jet Barrel and one on my .224 Barrel. Unless you are on a good rest or reall have your tripod on something sturdy, I have found higher magnification to be a problem.
All of these set ups hold nice groups out to more than 250 yards from a bench.
The thinking in the 1960s was that you could not make a pistol from a rifle action but why not make a rifle from the XP-100 pistol action and so the Remington 600 rifle was born. I have had 3 but this 243 Win. is my favorite.