Big City Marathons???

I'm currently starting to think about a fall marathon and was looking for some opinions on larger marathons.

I've done 4 marathons, and all them had under 2000 participants.

Chicago came up as a possiblity (some friends are doing it, BF has a brother there, I have a sister in Milwaukee so it would be a fun trip). But I'm a little nervous about the idea of being surrounded by 45,000 other people. (My last marathon was 3:54 so I would qualify for one of the start corrals which would help some.)

Any thoughts on larger marathons, or on the Chicago marathon?

Thanks :)

No thoughts on Chicago, as I've never run it. But I have done NYC 4 times and I had a blast. Yes, you were in a sea of people, but the crowds were just AMAZING! And all of the other runners from around the world really give that race an international flare.
That being said, NYC is NOT a race to expect a PR in or to BQ. Just too many people. And at a 3:45 you would be amongst a LOT of friends.
So I guess it really just depends on how much of a crowd you can handle. There is a big one at NYC. But the crowds on the sidelines are AMAZING!!!