I've owned both the R1 and Heavyweight Core, can't comment on the Peloton. I think the Core and R1 are pretty close to being the same thing, minus the camo option for Sitka. Weight is almost identical, the large Polartec grid is almost identical as well, even the fit is very close.
Both make a really good mid-layer on the move in colder temps, in warmer weather they could easily serve as an insulating piece. The hood on both is excellent. The fit on both is athletic (trim).
The Heavyweight Core is a critical piece to my hunting clothing system.
