I would look at a fast twist 223 Rem. Shoot anything from 40 gr varmint bullets to 80gr target bullets. Build a sporter gun that weighs 8.5 lbs. Since you already have the 243 starter, maybe the 22/250 with an 8 twist would be the ticket. Lapua brass is the best option. It's always available somewhere, and well priced.
I like the .243 cal as much as the next guy but they have too much energy to save hides consistently. Unless like Keith suggested your using very stout bullets.