I've only ever gone between 4 and 7pm myself, so I'm not sure what the volume becomes later into the evening, but it's a large space (so harder to crowd than a lot of the smaller spots in the area), and has stunning views looking out over Central Park.  

Another good option is the Campbell Apartment. It's at 42nd and Park (Grand Central). That shouldn't be more than a 15 min drive, but that depends how far west you are on 50th and traffic, of course. It's an amazing space though! Definitely worth a peek.  
http://nymag.com/listings/bar/campbell_apartment

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