You've probably just not had adequate bottom insulation in the past, and that's why you thought you were a cold sleeper.
Otherwise, your metabolism may have changed, but regardless, you were more than adequately insulated both top and bottom.
When making quilts it became very apparent to me that most people that experienced cold while sleeping at the appropriate ranges for their quilts, weren't insulating below properly. It's equally as important as top insulation, and most 3-season pads aren't adequate at freezing temps.
You'll probably be fine now with the Xtherm, and an appropriately rated quilt, i.e. a 30 degree quilt down to 30.
I've always leaned toward having more bottom R value than necessary, and I usually burn up in my 30 degree quilt even at 25 degrees.