I don't load 260 but I do use it's grand daddy and ballistic twin the 6.5x55, 120gr Ballistic Tips are fantastic, just be sure to keep them out the tasty bits because that bullet is violent! I like Nosler's pet loads they have always worked REALLY well in my five rifles, might want to give that a try. Here are a few I would give a go at. 120gr Ballistic Tip Hunter powder, min 44.0gr at 2877fps max 48.0gr at 3043fps, they had best accuracy with the starting 44gr charge. That would be my first choice. RL 19 would be my second, since that is what shoots so well in my Sweed, 43gr to start 47gr to top it out, at max you are pushing 2980fps from a 24" tube, much like the Sweed expect your best accuracy close to max with that one. H414 and W760 are the other top powders I would use if you like a little zing, both will get you 3,000+ in a 24" and probably 2850-2900fps in your carbine. Both are 41gr to start and 45gr at max, as with the RL19 expect you best performance at or close to full power. That is about all I can tell you about the 120s, if you want to know anything about 130s or 140s PM me
Nosler #6 is a worthwhile investment, easily the best of any of my manuals. Have not seen 7 on the shelves yet but I am sure it is every bit as good.