When I put together my F class rifles, I went with my 6.5 mystic which is my version of the 260AI.
Out of a 30" match barrel, I can push a 139gr Lapua to 2900fps with superb brass life and accuracy. This is pretty much the same velocity many 6.5-284 shooters use cause that is where these bullets like it the most.
I have just recently taken this rig out to 2400yds so there is little issue reaching out a very long ways.
So far, one of my rifles has digested 1800rds and is still printing in the 2's and 3's at 300m. I expect to get at least 2500rds out of it before needing a set back. That is almost double what 6.5-284 shooters are suggesting they get.
The 260R/6.5-08 is a wonderful rd too and if feeding from a mag, better then the improved versions. The only downside is that with the sloping shoulders, you can't run pressures as high without lots of case stretching. That does limit top end velocity. However, so much depends on your barrel that it might be a tie.
For a LR varmint rds, I would lean to the Mystic/AI versions. You don't need to run full throttle and brass life will be beyond your barrel's life. For a competition rd, I am not alone in enjoying success at extended distances.
Jerry