I have the non-zip off Helio's and they're warm. I don't have the Kuiu merino bottoms, but I do have their Pro Merino 200 top, and it would get the nod for me between the two.
The merino should in theory thermoregulate a little better, but I think both will be pretty damn warm unless it's pretty cold.
I like the Peloton 97 for anything active but still cold enough to warrant a mid on my legs.