If you think in terms of powder capacity to bore size, the .243, like the .270, is really a magnum cartridge. The double base powders burn hotter, and you already have a cartridge which is burning a lot of powder for the bullet weight, so you are going to be burning out your throat faster.
The .243 can be a superbly accurate cartridge with a wide variety of bullets. Play to that, and go for accurate loads first and foremost, whether for foxes, small deer or larger deer.