I just ordered a bunch of 'em for myself and the crew. Thanks Rich for the size comparison w/Montbell.
I'm about 5'7. 155 lbs, and I found I needed a M with the Montbells (ex-light, UL inner, light down), but a S in the Western Mountineering Flash (really, really nice jacket btw). These sizes fit me perfect.
Hope the EB small will fit me well.