Meanwhile back at the gloves issue........as another ex courier, and an all year bike user, I can tell you from experience that the more fingers your gloves have, the greater the chance that they will leak.
The only true solutions I have found, are either the handlebar muffs as mentioned previously, or a set of overmits from your local friendly outdoor shop. These are cheap (I paid £12 this year for a breathable set), and very durable baring accidents. Just wear them over a set of ski gloves, or heavy bike gloves.