I'd go higher than 46 if you like going fast and if you're got strong legs. I ride 50/16 - I love this gearing because I have absolutely no problems keeping up with traffic, but I can still get up to speed relatively quickly. When I first switched up to it, it was a little rough but I got used to it very quickly. It's not a problem on the bridges, but you have to put in a bit of work. Wind + bridge climbs can be a little rough but I love it otherwise. I ride a Cannondale CAPO, which I love, it's got a few dents in the top tube and I'm looking to replace the frame with the exact same thing if I can ever find one for sale in the right size. +1 on the bullhorns : that's the way to go. If you're pounding through pothole-ridden NYC streets with bullhorns I'd make sure that you have a strong stem. I've cracked stems before riding in the city, so now I ride with a MTB stem because I'm paranoid.

RE: dodging in and out of traffic: I like a slightly undersized frame that is easier to throw around between my legs - that makes me feel a bit more nimble.