Re: 375 RUM and the 260 Accubond...
Ball, fine grained and almost no flattening. Meters very uniform in a Lyman #55 or a Lee Perfect Powder Measure. The Lee may be at the upper end of it's capacity to meter that much powder as the 375 RUM can use about 100grs+.
In 30-06 Hornaday and Hodgdon do not require a magnum primer but anything that has 70grs+ of powder to set fire to I use a Mag primer.
It is a "tailored" powder meaning the Chemical Engineers gave it specific characteristics as to grain size, nitroglycerin content, deterrent coatings etc. so it works in a narrow range of conditions unlike, say, 4895 which has a broad application and tolerance. 4895 will burn well anywhere from 20kpsi to 62kpsi but Superformance is supposedly designed around 58kpsi - 62kpsi according to what I've read. Also read that as it is a new technology ball powder it is far less sensitive to temperature fluctuation than traditional ball powders.
In today's world we reloaders enjoy the best selection of components ever. When I started in 1971 there were maybe 12 - 18 different rifle powders and may be that many shotgun/pistol offerings. 4831 was surplus only from Hodgdon's and Alliant had RL 7 and RL17. Last time I looked there were 138 different powders on the market.
Don't rule out the Scandinavian powders, Norma or VitaVourri. They are different enough to explore and back in 1974 I had a load in 30-06 that tossed a 200gr pill faster than anything else with Norma 205. The pressure signs were nonexistent.
Superformance is on my short list of powders to try if I need something in a burn rate around 4350/4831.
Just my experience...