The 2205/10/Jubilees in the 80s were Marshall's first 'modded from the factory' amps. Then, the 900s continued that...Slash reissue in the 90s...then the KK 800, AFD, YJM....But I think we all want a real Jose fire breather like the artists all seemed to have in the 80s.
I think the SLX has the most gain available of all, except a few 2205/10s I've had are super gainy....but, Marshall started going cheaper on parts/filtering in the 90s just like they did in the late 80s to save money; so the 900s have a thinner tone in general vs the 800s, JMPs before them.
Might be a cool mod to try with an SLX, change up the filtering a bit and see what that would sound like.