Lise,
The lobster gloves, the ones made specifically for biking, are going to be better than regular mittens simply because they'll grip the bars better than other mittens. Not so much sliding around. I agree with Denise: I'd prefer gloves, for a better grip, but when it's extremely cold, the lobsters are better for warmth. That said, I wear gloves, no matter what, with liner gloves underneath for extra warmth. I have awesome PI gloves, a little large, so I can fit a layer of liner gloves as a base layer. It works for me...... if not, I'd go with the lobsters.
It was extremely cold here, too, for an early morning turkey day run! Probably very much the same as your experience. (I'm in Iowa.) Plus N winds of 15-20 mph. I wimped out! Did not do the local T trot, rode my bike on the trainer instead.

So I salute you for braving the cold!!!!! Congrats!! You are a braver woman than I.

annie