From my experience, both Varget & 4350 are too ‘fast’ a burn rate for a 75 from a .22-243AI. Anyone with Quickload and a clue will tell ya same. I run H1000 behind a 75, Retumbo behind an 80, and RL22 to fire form...
The reason 4350 works in the Creed(less) is because it’s quite a bit smaller in case capacity. About ~12%, depending on headstamp. Hence, the need for a faster burn powder to push a same weight bullet, from a case with ~12%LESS capacity than a .22-243AI. Basically, ya gotta push a 22Creedl(less) to its limit to just get close to a .22-243AI, on cruise control w/ the top down. Simply stated: when compared at a baseline case pressure, larger capacity cartridges win all the time, every time...
I get that there are many fans of the Creed(less) but you’ll find that some of the cheerleaders have ‘skin in the game’. Happily, I’m not beholden or constrained by any business venture(s) so I get to use and cheerlead for what works best for me, and me alone.
Haven’t tried RL26 in the .22-243AI, but I suspect it’d beat H1000 in speed. Because, that’s what Alliant powders do! The H1000 is just so forgiving and temp stable, that I don’t bother to mess with a really good thing. Plus, I’m saving my ‘26 for something much more nasty

Again, the AI is GREAT because you can use a plain ol Redding .243AI type S die (with proper bushing) to load for it. And the seater works, as is.” for heavy .224 bullets. Nothing proprietary about the .22-243AI it is 100% ‘open source’ and just plain works a treat!
P.S.
yup RPM is up there, reckon ~325K for a 75 from a 1:8. But an 75 -80 AMAX / target VLD, in that window have proven to handle that stress and still perform great, terminally...
Have fun!