Critical Multiplier

Whats the max of main hand critical damage multiplier?

There's not enforced maximum cap, if that's what you're asking.

Pretty sure there's a quote from Mark somewhere saying critical chance can't go above 95% or below 5%.

That's chance, he's asking about damage %. You are correct, though, it is a 95% cap on chance and a 5% floor.

No hard cap on damage, I hit over 700% in legacy on a discharge build, definitely could go higher with all the passives around witch/shadow (and the right gear).

Yep, somehow I saw "critical multiplier" and read "critical chance"... I blame lack of caffeine.