I tested my neoprene gloves last night on a 5.5 mile ride. Temp was in the teens (F) with a brutal headwind the whole way. Early in the ride, I was noticing slightly cold hands, particularly the pinkies. By the time I arrived at my destination my hands were sweating (as were head & back). Next time I will try them with liners, as they start feeling a little clammy with the sweat in there. The work a lot better than my ski gloves though, which are a little 'poofy' and catch on shifters / brake levers. The neoprene is more streamlined & still windproof. But does not breathe at all!
I use over sized neoprene gloves with wind blocker fleece gloves in side. They work for me down to the high teens. They can be a bit bulky at times when shifting and braking at the same time. Like Koffee said if your hands start to sweat they will freeze.
My Castelli T-Tech gloves are kind of like neoprene. My hands usually start out a bit cool, and the tip of my index finger and thumb can get pretty cold at first. However, after about 15 minutes they're fine, and may even sweat a little bit by the end. So far I haven't run into any problems with the sweating. A glove liner definitely does help.
It was -19C/-2.2F with windchill -40C/-40F in Montreal yesterday, and I was quickly too cold in my new five finger Kombi gloves which I will return to Mountain Equipment Coop.
Today was -28C/-18F, with 13-30km/h winds bringing it down to -38C/-36.4F, and I was fine riding around for over four hours of start and stop errand running in Craft three-finger claws with cheap Auclair fleece liners.