Never heard of 85 ssi cap, but I assume that's if you're a Hardcore pvmer, and you do a lot of Grizzles where it Reduces your SSI by -60%...
I've checked some of the calculators for SSI, can't bring myself to believe they are right with SSI vs Dex/stam speed increases.
If you have a 4 second weapon, and have 50% SSI on your suit wouldn't you be swinging at 2sec with 0 stamina?