Stealth at 50 comp is all you need no advantage over 50 AFAIK, now if you spec 50 stealth you will have the fastest movement speed . Most use 35 stealth and keep it even past rr5 for the movement speed, if you lower your stealth you lower your movement speed.
i tested it in beta. At lvl 50 all you need is composite 50 stealth. There are break points in free mos movement, 40 seems not much diff than 50 BASE stealth, mos is calculated from base stealth.
The only thing i never tested was stealth over 50 vs monster level for reveal. On live stealth over 50 was compared to monster level in a formula (i think) and more stealth helped to not be revealed by guards and mobs over 50.
I could be wrong about the over 50, don't know how it is here.
But vs players based on my testing-- 50 is the same as over 50.