It's a great powder in 10mm. 165 gr. 10gr 800-X will give you 1400 and a tad. It's a hard to meter powder because of large flakes but my Redding BR-3 throws the charges spot on. So much so that I stopped weighing the charges after the first initial 3 charges. I've been loading the 10 since it was born and it's my choice of powder for top velocity in medium to heavy bullets.
Lots of people like 800X for the "heavy" loads. Lots of other people hate the fact it meters like paper plates. I'm a freak about such things and so weigh every charge of everything rendering metering concerns moot.
If there's one thing I've become certain of it's that there's too much certainty in the world.