powerstretch vs merino

I have a pair of microwt (150gram)merino tights and a pair of ltwt (190gram) merino. Also a pair of terremar silk long johns. Weights are 5.75oz, 7oz & 3oz respectively. I'm looking at a pair of power stretch pants (Mountain Hardware, Wild Things) at 7oz and wondering is it would be worth the money? Any experience w/either? Or could I get the same warmth from a combo of what I already own? In my experience, fleece drys a bit faster than merino. I'm looking for a mid-layer for cold (below 20F) for active pursuits (running, snowshoeing, etc.) to wear over the silk base layer. Probably rules out the PatR1 tight as too warm. (I have the R1 hoody)

Thanks.