I have no advice for you on the steady hand 2 bit, as you are correct (the former calculation -100%/120%) and I've never seen such a failure personally (having leveled all but 1 crafting class to 50 -- ALC is currently 30).

I can tell you though that the condition (poor, normal, good, excellent) only affects quality enhancement (basic, standard, advanced, and hasty touches, as well as Byregot's Blessing). Careful Synthesis (or any synthesis as well as piece by piece) are completely unaffected so you'll get the same results under any condition. The only thing that can increase the potency of your synth skills (other than stats, of course) are the ingenuity buffs (which will not affect piece by piece).