Looked up my 7mm-08 data. 31gr of H4198 made 2,550-2,600 with a 120 TTSX in a 20" factory 7mm-08 Rem 700. The manual went up to 32gr. If I was looking to shoot something around 120-123gr in a 260, I'd load a few each at 29, 30, and 31gr. I'd then shoot over the chronograph and keep an eye out for pressure. You should be able to make somewhere around 2,500.
