From 50-54F, I go with 3mm gloves that fit like a glove. Little to no wiggle room in the fingers length or width wise and equally important, a good sealing wrist cuff. Either a velcro wrap w/o a plastic buckle (like Aqualung's Aleutians), or a tight wrist seal like the ones seen on O'niell surf gloves or Scuba Pro's Everflex gloves.
Having gloves that have little squish factor at the fingers helps too. So look for kevlar tipped fingers, tool dip your finger tips with Plasti-dip, or get thin gloves (not really a comfortable option for you).
Keeping water transfer in and out of the glove means warm hands, assuming you have good circulation.
At your temp range, I would recommend upgrading to the 5mm; but still keeping with the above requirements which will allow to keep some amount of dexterity.
If you get a glove that doesn't actually fit like a glove (loose material, wiggle room in the fingers and palm) you'll can lose most or even all your dexterity, no matter what thickness. Just keep that in mind.
With a proper fitting glove you should be able to write notes and tie your shoe with a little practice. Granted it will still be a tad bit sloppy, even when you get good at it.