Re: 6mm Remington
It always depends on your application, but for all around duty, it is hard to beat a 6mm Remington; plain vanilla. My first was a Remington Model 660, and boy, I wish I still had it! (stolen) Had a few 243's and 6's since then, they're all good.
Plenty gun for medium to long range varmints. I find the most useful bullets to range from 75 to 87 grains, but did manage to kill a kudu with a 100 grain Sierra from a modified Model 600. Ran a bit, but one shot.
This is just personal opinion, but if you are looking at 6BR or 243 AI or any similiar version of the 6mm Remington, I'd stick with the factory cartridge, perhaps with a tight neck, OR if you want more speed, with less barrel life, the 6/284 is a logical choice.
No hassle, no special dies, good performance, excellent barrel life, good resale.
Good hunting. LB