If it was me---- I would look to go 6.5x57AI that is if I wanted to increase velocity. I would need to check to see if the 57 case will function in the short model 70. And I would go 24". That is what I would look at. But the 260 case will not be useless by any stretch of the imagination.
Bullets ---95 gr. Vmax for all things varmint and any of the 120 gr. to the 130 gr. hunting bullets for all things eatable. It should do everything my 6.5-06 does out of a short action. You might need a larger freezer.
8mmwapiti
I can address several of the points here, as I have built them.
My favorite cartridge is the 6.5 x 57. Unless you are using the lighter bullets, you are better off going with a long action. Sort of the same reason, a 6mm Rem is a total different animal in a long action vs short action. Seating the bullet further out increases velocity potential substantially.
The 260 or AI version will feed just fine thru a Short action Model 70. Am in the process of doing two of those now. a heavy magnum contoured barrel in 26 inch and a varmint contour also in 26 inch.
