johngenx, there's still a lot of air in those mattresses, no matter the primaloft of the BA or the ducky feathers of the Exped. Air is air, and the prima/feathers only go so far.
You're giving up some insulation for the sake of comfy, oh so comfy!!, sleep. My solution was to also carry a thermarest (ok, I was testing the combination) and then try one night without the thermarest layer.
I could tell the difference!
I would not risk going outside in the next few months (before the snows stay) without at least a foamy or thermarest ground layer between my exped and my tent. And as for winter, well, the thermarest will be definitely part of my kit.