Not trying to be a total smart *&#, but the phrase "good cold water wet suit" suit is an oxymoron...like fighting for peace, or military intelligence. I have been diving since 1960, only a regular sport diver, and have had many wet suits, made from different materials, and different configurations, IE. Farmer John with shorty underneath; Over thickness, skin in (no nylon on one side and use baby powder as dry lube so it'll slide on) and my latest is the infamous titanium. Some were stock off the shelf and others were custom built.
Here are my objections. Wet suits are restrictive in nature. Yeah! They've gotten better but there is still lots of restriction. Unless you are wealthy enough to own a motor home, you'll always put them on standing in the cold and you'll take them off in the cold with your skin wet from the dive. You'll have to find some place to get out of your wet swim suit after the dive without getting arrested. And in 'cold' water, you'll still be uncomfortably cold in an hour or two. Specially if you are metal detecting. You don't generate much body heat while detecting with SCUBA. Fewer muscles will be used underwater than on the surface for the same amount of area covered. About the only part of your body that is working hard is your right arm. You sweep and then fan.dig with that arm to recover the goodies. The rest of the body sort of moves along with the upper. You'll probably do more of a low crawl on the bottom rather than an actual swim. In contrast if you were sport diving seeing the sites, you'd be kicking with the fins and generating some heat.
Here's the solution. GET A DRY SUIT! They are more expensive, but you can crawl into them in the middle of the mall without offending anyone as you'll have on thick pajamas or your street clothes. DO your dive. Come out of the water and peel your suit off and put on a jacket.coat, warm and dry and drive home to your next place to try.I am going for a used suit. There are lots of them out there and they can be had for about the same price as a good wet suit. They require maintenance on the seals but you can do that yourself without sending it back into the manufacturer for a big repair bill. Hope it helps. Just my opinion but I'd be interested to know if money wasn't an option, if anyone who cold water dives would PREFER a wet suit. Later ...Jim