I have used varget powder for the 107,123,and 142 SMK when I shot hi-power silhouette. For hunting I load h-4350 and 120 gr. berger BT have killed a mule deer buck and a whitetail doe so far and both were one shot kills. I think for Pa. the .260 is the closest thing for a all around round that there is.
I agree this is one fine cartridge if not the almost perfect whitetail cartridge...in a great custom chamber job it makes an awesome long range cartridge, my wife and grand kids use them with nice results...all three of them use H-4350 for fuel, tried lots of others but none produced better results over all..they all use the triple shok bullets and have never lost any deer. It's a big hit on tactical matches and sniper matches, those long sleek bullets with high b.c.'s really fly nice once the distances stretch out...just buy yourself a few hundred cases for the long run!!
I have a 260 being built right now. My research tells me that H4350 is the go to powder for the 260. Also, Hornady just came out with two new 6.5 bullets. One is a 140 and the other is a 143. One is a match bullet and the other is a hunting bullet. Lots of research went into these new offerings and so far the results in the field have been very impressive.