By arguing that a loss of 200 fps is meaningless, one can argue one's self down from a .300 Win Mag to a .32-20 for all North American big game, 200 fps at a time.
I like the way you think.
I've found a slightly more prosaic way of looking at it, and that is equating velocity and distance. If you theoretically knock 200 fps off the round, it is roughly the same as shooting the same animal at a greater distance. Take 200 fps off a 308 WIN round and it's about the same as shooting the animal at 75 yards greater range. Take a 300 Win Mag and knock 200 fps , and it's about 100 yards difference.
You can also equate two different chamberings. Given the same bullet, a 180 grainer, a 30-06 has about the same at the muzzle as a 300 Win Mag at 100 yards. At the muzzle, a 30-30 with a 170 grain bullet has about the same velocity as a 300 Win Mag at (let me take off my socks. . .) between 300 to 400 yards.
