Does a little bit bigger bullet going a little bit slower enough to correct for this? Nope. But then again, either does a .300 mag.
And did I say that? Nope!
Besides, you need to pull out your loading manual and study a little. 7mm-08 in the 100gr range travels a good bit faster than a .243 in that same weight. 100gr .243 and 120gr 7mm-08 travel about the same speed.