If you are into Hornady ammo, the 140 ELD-M #26331 and 147 ELD-M #26333 shot accurately in my 24 inch barrel 10T-SR 6.5mm CM and in both of my model 12 26 inch barrel 6.5mm CMs.
The Sierra 142 SMK and 130 TMKs also shoot well in all of my 6.5mm CM rifles.
The Hornady 143 ELD-X #2635 is a great hunting round with a high ballistic coefficient and shoots just a bit less accurately than the match rounds.
The 24-inch barrel version seems to like the 130 and 140 grains better than the heavier bullets. It is just the opposite for the 26-inch model 12s.
Every barrel has its own preferences and other people's 'pet loads' don't matter to your specific barrel unless you are really fortunate to match up with a barrel that has the same preferences.
H4350 and IMR4451 Enduron are both extreme powders that are very temperature insensitive - that's a plus if you are planning to shoot under a wide range of temperatures.
IMR 4350 works great for all three of my rifles as does IMR4451 Enduron powder.
My 24-inch barrel has a slight preference for IMR 4350 over IMR4451 powder.
Reloader 17 seems to work best with the 130 grain bullets.
Varget, IMR4064, H4895 and VV N140 don't shoot as accurately as the slower powders.
They shoot OK but I am an accuracy nut and strive for every bit of accuracy that I can find.
Again, that is what my barrels prefer - your barrel might be totally another case.