I really like the 25-284. It's built on a Winchester length short (Medium?)action (Montana 1999) 3.125 Max OAL. It's throated quite a bit longer than possible with a Rem short action. It pretty much duplicates 25-06 performance. 100 grain at well over 3300 fps & likely more juice in reserve, but the long brass life is nice at sane pressures.
The long Rem action may
feed the '06 case better, but for accuracy there just may be something to the shorter, larger diameter case of the -284 based rounds.
Either one necked to 6mm ought to really smoke, though I personally like the 25 or 6.5 bullet choices better for hunting, the 6mm Barnes will surely knock the stuffing out of any critter likely to be encountered & the lighter varmint choices are likely to be pretty spectacular at warp speeds, though probably not too long on barrel life..
If I was able to do it over again, the 6.5-284 would get the nod, just because of no necking down & a few more bullets coming available in the past few years. Just getting old, I guess.