Id say 300 fps from 260 to a 6.5x284 then a 400 fps jump up to a 26 nosler
With that added speed the 26 nosler is in a different league
My 260 Rem with a 22" barrel shoots 130 class bullets at 2900+. My 6.5-284 shoots 140 Bergers at 3072 on a good day with a 26" barrel.