Keep this in mind. There literally is zero difference between 6.5 calibers. There might be a few hundred feet per second but for all practical purposes there is little to no difference. The biggest reason there are so many calibers is so gun manufacturers can sell more guns...........well and there are a bunch of crazy butt guys that like to build wildcat cartridges. yeah my father in law is building a 7mm wildcat cartridge that is based off of the SAUM with some modifications to case length, width, and shoulder angle. All to shoot tighter groups at longer distances.
The accuracy of any of the 6.5's is great. Speed varies a little but with range finders it doesn't make any difference for most practical hunting applications. So the short answer is.........Get a caliber that you can deal with the easiest and shoot it. I went with the 6.5 X 284 for two reasons. First it is on the hotter side of the 6.5 cailbers and will do well in a bunch of shooting applications. Second, my father in law has all the bench rest quality reamers, dies, bushings, equipment, ect to reload this caliber. I didn't have to buy any reloading equipment for this caliber.