I'm not so sure...I've compared the load data on it to several others...you may be right about the burn speed being RL25, but I believe its a double base powder...mainly because it also does really good with lighter bullets (140 grains)...most single base powders aren't that versatile, or energetic.
Myself, I believe its burn speed is in the range of RL22 and MRP...not quite as slow as RL25...if I'm right (IF), 7977 will fill a gap that needs filling...that is if it lives up to the advertising, there is no temp stable powder in that burn range...H1000 and Retumbo are both too slow for rounds like 280 Rem, 280 AI, and others with similar case capacities and 140 grain bullets (270 Win), and the 25-06 with 90-120 grain bullets....according to the data, 7977 is right at home there.
It'll give us a powder that doesn't need 114% load density to get good speed...being able to keep the load density below 107% is worth something.
But thats all just my hypothesis based on load data comparison...could be all wrong.
I look forward to trying 7977 in my 280 Ackley...and will happily buy a pound when I see one.