You'll likely NEVER notice the difference unless you're a very dedicated varminter-and most of these guys aren't going to be shooting factory rifles if they even shoot standard cartridges.

Here's the skinny on the difference: Say you shoot a .22-250 and a .243 parallel to eachother at the exact same time against a crosswind, as your bullet flies, it's going to drift in proportion to the windspeed-if the bullets effected the same air resistance, in the same period of time they'd drift laterally the same distance, but the .22-250 is a bit faster, so say in a half second they laterally drift 2", in the same half second, the .22-250 flies farther, so if you checked them at the same range, the .243 would have drifted farther-same principle proves why faster=flatter shooting, gravity and wind effect them the same per amount of time, not per distance, so faster should fly straighter....BUT, the .243 has a considerably heavier bullet (usually, some people shoot 55grn's in both of them), a heavier bullet has more linear momentum, Newton's law, object in motion wants to stay in motion, like pushing a rolling marble off course as opposed to a rolling bowling ball, the heavier it is, the harder it is to push it off course...so a heavier bullet is less affected by the wind.

At long ranges (about 400yrds and out), the momentum theory wins out, wind gets a BIG hold on little bullets as they get way out there...ranges most guys hunt at, you'll probably never notice the difference.