I haven't gone there yet with rl26... I have worked up a 140 grain load for my last 7stw barrel that shot well, but haven't bothered to shoot it through my new 7stw barrel. My 2 300rums are shooting rl25 and 180 hornady pills at present. I was also shooting rl33 and 225 hornady pills in one of them, but the barrel is going south (time to re-barrel) and the load stopped shooting well in that barrel. I haven't had time to work up a heavy bullet load in the new barrel but rl26 will be one of the choices for powder.
In the old 7stw barrel rl26 seemed to be faster with a couple of percent less charge weight than rl25.
rl26 seems to be a good choice for a mag. powder that isn't creeping in on 50 bmg powder speeds.