It's hard to beat a 125 grain Nosler Partition, or a 129 grain Hornady, on top of 47.0 or 48.0 grains of Reoader 19. The 125 grain Nosler is my favorite bullet for the 260, and it's what I use for most of my hunting (deer, elk, and bear). If there's any concern about recoil, try the 100 grain Nosler Partition with 49.0 grains of H414. It makes the .260 feel like a .243, and the 100 grain Partition is plenty for deer and pronghorn.
The heavier 140 grain Partition failed to expand at ranges of 200 yards or more when I tested it in a T/C Encore 24" .260. The tip expanded very little, and unevenly, causing the bullets to tumble in wet newsprint. They all ended up going backwards, and then shedding the rear cores. The rear cores actually held together and penetrated a little more, even mushrooming a bit. I think the 140 grain Partition needs to be launched from a round that has at least the case capacity/velocity of a 6.5-06 or .264 mag.
All the other bullets that I tested did great in the .260, although the twist in the Remington barrels is a little slow for the real heavy 160 and 162 grain bullets, so 140 grain bullets should be considered a practical maximum in a Remington M7. 140 grain Speer Hot-Cor, Remington, and Hornady IL bullets all worked great in both my .260s.
For varmints, I like the Speer 90 grain TNT with 50.0 grains of Hodgdon H414.