I have loaded 120's for 3 different rifles in 6.5 Creedmoor. Two bolt guns and one AR. I have tried about a half dozen powders although some only with the 123gr bullet.
In my AR currently I use N150 and the bolt is loaded with AR Comp. The AR Comp load has low recoil and getting about 2900 fps with the 120 AMax.
I have a customer who is using the AR Comp load with the 120 AMax and in the past few weeks they have taken several antelope in New Mexico with good results.
If you want top speeds I would try H4350 or Reloder 17 which has given the highest velocities for me so far.
Hornady loads the 120gr AMax Match ammo with Varget which did very well for me too.
I have a bunch of H4350 on hand, but nothing else suitable for the cartridge. Looks like I have some shopping/searching to do for powder, huh?
VENATIC: There's nothing showing for loads with AR Comp on Alliant's website. Did you use .260 loads as a starting point?
I likely won't be using this rifle for anything past 400 yards (actually 300 is probably more realistic) so I'm leaning more and more towards 120s and probably won't ever load anything heavier unless my son decides to go to Alaska .....
It's likely going to see service as a pronghorn, pig, or elk rifle.
I used Varget and 120ELD's and 123ELD's. Worked very well at 100 to 300 yards. I also used it with Speer 100 gr. HP flat base. Nice load and just as good as 123 ELD's. All loads to Magazine length. I tried pushing them to longer length but didn't make a difference. Also used 4451. Did't see any difference from the Varget.