You kind of answered your own question, you said "how many high powered rifles".

And now there are some very comprible bullet/sabot rounds to use in them instead of the old Fostner slugs. Many of the newer rounds use the exact same bullet as you would find for a muzzleloader or even a large caliber standard rifle so those have comprable BCs. Yes, a "lunker" slug does have a lower BC so it looses velocity at a faster rate, which also gives it a larger drop at a given distance, but you (not specifically you, but in general) cannot compare a magnum or high powered rifle to it any more than you can compare one to a low power loadused inanother standard rifle.
It's like comparing a 50-70 to a 7mm Weatherby Mag to a 500 S&W, especially when using completely different platforms to fire them.They are each in their own class and do not work the same in all situations, but each has it's uses and each has it's advantages over the others.