The Nosler 26 is .264 or 6.5mm caliber, the 28 is .284 or 7mm caliber. Both have large cases and burn lots of powder to be among the fastest of the cartridges of their respective calibers. The 26's main advantage over the 25's CC mentioned is it's ability to throw a heavier weight bullet with a great BC for very long range work. I use a 25-06 or 280 (.284 caliber) for pretty much everything I hunt, both based off the 30-06 case, which has less powder capacity the the 26/28/257wby. This also allows me to get great performance from a 24" barrel, the bigger mags need a 26" barrel, at least, to reach their full potential. If I want to prepare for very long range stuff, I take my 280. Difficult to find high BC bullets in the 25's.
Both the 300 Win Mag and 300 Wby use .308 bullets. Most would probably say the Weatherby may give better velocity, both are great rounds. A 7mm Rem Mag uses a .284 bullet, but can achieve velocities right in there with the 300's with a lower bullet weight. There is not an elk walking the earth that is likely yo know the difference between a 180 gr. bullet from one of the 300's, vs a 160gr. bullet from the 7mm, with bullets of the same type.
I think what you really need to decide to pick between the various offerings in a given caliber is; how far will I shoot? The further you plan to shoot, especially if past 500-600 yards, the better the fast rounds that can throw a heavier bullet look, which is where the .264, .284 and .308 caliber bullets have an advantage over the 25's. This is due to many factors. For myself, my 280 has excellent accuracy and adequate velocity to insure bullet performance further than I will shoot. My limit is 600 yards under ideal conditions. Relative to the 7mm's, for me the faster 7mm's, while great rounds, are just a waste of powder, money and make more noise...than my 280 and come in a larger less handy package that recoils more. You can make the same analogy about the 300's vs the 30-06 as well. My two cents anyway.
