I've found gloves that are 3mm or thicker cause my hands and forearms to fatigue quickly. 2mm gloves with a smooth skin and radically curved fingers are absolutely perfect imo. I can use them down to about 3*-4*. I also prefer the dexterity and full protection of a 5-finger glove
The best ones I've found and I'm currently using are from Ride Engine... http://www.rideengine.com/GEAR/Wetsuits ... ves_2.html
Prolimit's Utility glove is a close second, but I don't like (nor need) a wrist strap. It's unnecessary and a hassle to put on/take off. However, the last gloves that had straps, I just cut them off. Problem solved!
Ion's Claw glove would probably be better suited for 0*-3* conditions since it's 3mm on the back of the hand, but still 2mm on the palm to reduce fatigue and maintain better feel.
If you want to go a bit thinner, Gul's Windward glove is similar in design with 1.5mm neoprene.
The main theme here is the radically curved fingers. I feel this is the most important feature for both comfort and performance in a 5-finger glove.