Wow, it's been awhile since I visited this board, but it's a slow day at work, so I'll help out. I can't speak for the NY area, but I'll give you my insights into Boston.
I'm originally from the St. Louis area (pm me if you want to know my high school) and am currently working in Boston. I know a few people who went to SLU law and then moved to Boston. From what I understand, they weren't too successful and have since moved back.
The problem is that the Boston area is inundated with law schools. Suffolk, Northeastern, BU, BC, New England School of Law, and Harvard. From what I understand, the UMass system has recently announced that they will be opening up a law school. That's seven schools' worth of graduates with whom you would be competing. Granted, Harvard grads can go anywhere as well as a handful of BU and BC, but Suffolk and Northeastern are very local.
Moreover, it's hard to break into the Boston market if you don't have any ties to it. It's not nearly as bad as trying to break into the Stl market though.
If you do well at SLU (i.e. get top 1% as you imagine), then I would just transfer after your first year. But as people will undoubtedly emphasize, you cannot rely on transferring. If you want to stay in Stl but want to work in Boston or NY, then go to WUSTL. It places well in both cities.
Hope that helps.