I've been using the Hades' Flamemaker. Only my wand has been losing its percentage. The gear hasn't changed..
I believe that has double crit ratings - 40 universal rating which would give 5% at level 90, but 4% at level 100, and 86 fire rating, which I think is 14% at 100. In any case, for every 10 levels your wizard go up, crit goes down 1% per rating.