Only you know your threshhold.
If you can hack it, suck it up and hold on if you can. Especially if the alternatives you're thinking of are finance-related (as a banker I'm sure you know firsthand how bad it is out there). It's ugly out there. I wish I could tell you otherwise, but suck it up if you can, and then quit when (or if) you get into Columbia (you find out pretty quickly actually if you submit for Early Decision - before Christmas). And once you're in, you can say adios to them and go on a boat cruise around the world (hookers n' blow are optional - I'm kidding, or not).
However, it it really is so bad that it's torture, first thing to do is to hold on for dear life, and try to find another job before leaving. Whatever that job is, I don't know. That's unfortunately something you need to figure out.
As for how adcoms will see this -- it won't really impact the application either way, since they're evaluating you based on what you've done to date as well as your future goals, knowing that whether you're at your current job or you're about to quit, the next 9-12 months are a transition period anyhow before b-school.
In other words, don't worry about what adcoms think, and worry more about your own current situation.
Alex Chu
alex@mbaapply.com
www.mbaapply.com
http://mbaapply.blogspot.com