I've only killed 30 deer or so, with everything from a stick with a razor to a 12 ga slug. the few I took with a .30 cal rifle went further than ANY I took with my .243 I'm a stickler for shot placement though.
The 30 cal is probably a bit too much for you from a recoil perspective. Recommend you stick with a 6mm round.
You're joking, right? You're just messing with Ryan I assume.
I forgot my , but not sure what else would make one a better killer with a 243 over a 300 all things being equal.