I have both and have worn both extensively. If your "mid" layer is more often going to be your exterior layer, then I like the 210 for the pockets. Both excellent pieces. The 210 is a little better with a backpack on too as the insulation is mapped, thinner on the back etc. The 200 is a bit lighter, my large 200 is 10.25 oz where as my XL 210 is 12.2 oz, the 210 is a smaller fit than the 200.
I think the 210 tends to be a little warmer if worn as an outer mid-layer and blocks the wind a bit better than the Peloton. At this point I find myself preferring the Pro Merino over the Peloton though.