243 throat geometry isn't great for heavy match bullets, and if it was, prob too long for 95% of short actions out there.
6cm is the easy by button as there is no ammo at LGS for a 243 with heavies. Lots of 6cm options. Personally I'd want 7.5tw in either, so any these 8tw 243/6cm options would be non-starter for me.
I'm waiting on my 6saw reamer. Basically a long necked 6cm that 2.015 case length. Holds same capacity as 243, but doesn't have the short neck and low angle shoulder, 0.150 Freebore will be fun. Hoping for 3k fps top end from a 20in barrel wirh the new 115-117 tmk.