from the info I've gathered so far, there are reasons to err on the small side. Smaller boards are easier to handle and turn, so better for beginners. They are just fine for mostly groomed, icy conditions (a la good ole East coast usa), but perhaps would not be good with a lot of soft snow. And of course they are better for people that ride in the park.
The first two apply to me. I'm 5'10, 185# and use a 157. Maybe some day I'll be in the park. And maybe some day I'll try a longer board and love that more. Time will tell.