I've been mulling over the same decision, I have a 260 and a 270 in sporter weight rifles and a heavy gun in 25-06AI. I'm trying to cut down on calibers and I also shoot a 308 win and 338-06.
In my opinion(key words) the 260 just can't compete ballistically with the 270 despite the higher bc in effective hunting ranges. Do some homework, get out your loading manuals and do some calculations. For instance in the berger manual, both shoot 140 gr vlds. The 260 has a bc of .612 and the highest "published" velocity of 2700, the 270 shoots a 140 vld with a bc of .487 at 3000, given a 2" longer barrel. The 260 drops 10.3MOA at 500, th 270 drops 8.6MOA. Even at 1000, the 270 drops 28 for the 260's 31moa. Please correct me if I'm wrong, I have nothing against the 260 and am not looking for a war. Try a barnes 110ttsx at 3400-3500 out of the 270, that's hard to beat for flat shooting, even from the magnums. There is also the nosler Accubond LR with a .600+ bc, altho it has not been proven on game. For those reasons, i'm leaning toward the 270. The 260 is far and away more popular in competition and heavy match prefit barrels are easy to find. Not everyone sells profit 270 win varmint barrels, so the cost may be more. You could look at a 6mm remington and get 243AI performance and factory dies and ammo also.
Being you have a long action, I wouldn't give up 200-300fps for a short action cartridge. You really have to rate whats most important to you: flat shooting, accuracy, barrel life, cost, etc.
Ps: I will be selling my shilen stainless select match 25-06ai with dies and brass if your interested.