The 6.5c looks impressive for the long range (1,000+) but I hold out on the new whizbangs personally . If it’s around in another 20 years I’ll think about it.. your 243 will do everything you want for varmint and some ! If you need more umph a 308 is never bad to have around and there’s tons of data on the cartridge as well as huge supplies of various ammo.

If you reload the 243, it’s in my opinion the most under appreciated long range round! Most of the commercial loads are setup for smaller shooters/smaller game. You can roll some hot 243 aka (6.5mm) and not need the 6.5c