My standard rifle in .260 Rem. has a tight chamber and peak pressure is reached with loads approximately 2 grains lower than those published in reloading manuals.
I started with IMR4350 for 140 grain bullets because that is what I had at hand at the time and 39.3 grains produces the best combination of precision and knockdown in my rifle before signs of high pressure start showing. I am in the process of developing a load using H4350, since I also have some of the stuff on hand and, unlike the IMR version, it is very insensitive to our summer heat. We shoot matches while the temperature ranges from 95 to 110+ degrees F.
36.0 grains of Varget also produces the same results with 140 grain bullets and is insensitive to temperature variation. This load also works extremely well with 107 and 120 grain bullets.
My Sako AII standard rifle in .260 Rem. also likes 36.0 grains of varget with all bullet weights and likes 40.4 grains of H4350 with the 140s. If I had to stay with one powder, I would stick with Varget.
Best of luck,