Benjamin 177 Marauder SSG tuning. 900fps possible?

Ok guys, update. I am using the Tim hill light valve spring, about 1800PSI on the reg and an Airgun Revisions lightweight hammer setup and am hitting 20fpe with a 10.5gr pellet and its very consistent and such a pleasure to shoot! I get a solid 50 shots, maybe 60 before falling off the reg as well. I might buy the Huma quick fill adapter and it may solidify a few extra shots to make sure you can get a full match without refill.
Made this into a different gun and one of my favorites now. Cheap upgrade for the results too.