I've just started using it in my 280ai, but it's the only powder I've tried with that rifle (it's a fresh build). I saw some guys on the Nosler forum did some temperature testing, I recall it was quite favorable, but not sure how extensive the testing was.
This type of testing (comparing velocities against other powders, or temperate sensitivity, etc) take quite a bit of time (and money in components). I think RL26 has only been out for… maybe 1 or 2 years???
What I like about RL26 is you can get a full charge with a somewhat lower load density. I use Redding competition seating dies, so I can't use compressed loads. I think velocities are slightly more then IMR 7828ssc. At least in the 280ai.
One other thing. Careful of Quickload predictions. The burn rate is pretty well off, you you might end up going over pressure if you trust that software (the burn rate needs to be calibrated). From what I understand, it's closer to RL22.
Anyway that's all I know. It's been working out well for me so far, but I've only started.
good luck!