Re: .260 Rem. Input
I had a .260 Remington about 14 years ago and where mine was a single shot Encore pistol with a custom barrel set up I had to handle it's loading a bit differently than you will with your longer barrel. That being said, I shot mine from a bench and off bags and fired the same bullet weight range that you have indicated. Mine had a 1-9 twist so the 140's weren't as accurate, but still grouped around an inch at 100yds.
H4895 was the best choice for my pistol due to the quick burning required for the 14" bbl that it had.
You would be best served with WW760 or H414 (they are the same thing) or Hodgdon or IMR 4350. They are slower and you will have the more desired case capacity to fill ratio. There is no reason that either one wouldn't group out of that rifle. I'd stay away from any thing slower than 4350 or anything faster than 4895. There are several good powders in that spectrum with BL-C(2) being a good one. Anything a .243 Win or a .308 Win will eat, a .260 Rem can shoot too.
It's a great cartridge and easy to load. I have it on my list of cartridges to have and will get another one made in the future.