The 6.5x55, which is a ballistic twin to the 260 is good for as far as most people have any business shooting. At 2,700 most bullets retain 2,000 to at least 400 yards. I have made a couple of 350ish yard shots on pretty big mule deer and have had dead deer and exits with 140 NP. It works on elk fine, but you have to keep in mind (in my opinion anyway) that while it is an adequate elk cartridge, there is not a lot of margin of error for being any more than adequate.
You are right, shot placement is the key. The 260/6.5 Swede are low recoiling, accurate, and easy on the shoulder, and thus easy to shoot. Easy shooters putting a 140 bullet of the proper construction in the right place are better than a heavier bullet ill placed.
