krochus,
I agree with you on some of that....powder has to burn to release its energy, but different powders release that energy at different rates of speed (burn rates).
You mentioned Varget and top levels of performance...You will get more speed from RL19, IMR4831, N550.
If you don't believe barrel length and powder burn rate go hand in hand, all you have to do is look at Sierras single shot handgun load data...they list 6 powders for the handgun loads...For the rifle data, they list 21 powders, with the slower powders giving the best velocity.
Some powders are more versatile than others, and Varget is one of them. Varget's burn rate varies depending on load density...In my experience, the hotter the load, the slower it burns.
Reloder 15 (my personal favorite) is also versatile...even more so than Varget. It gives good results out of short or long barrels.
And you're right...I used a bad example (25-06, 270) because they do use very slow powders. But I still stand by what I said, slower powders like RL 19 will give better results (more speed) than the fast ones in 30-06. RL19 in a short 308 don't do so good....
With powders that are ideal for it, the 308 can get up to 2750 FPS with 168 grain bullets out of a 20 inch barrel.
I like the 30-06, I have 2 of them...but the 308 is better in shorter rifles. Its a more efficient round...it nearly matches the 30-06, and does it with several grains less powder. Its also easier on barrels (because of the lighter powder charges).
We are both right...we just don't agree on it.