I just went with an XTherm at 7.3 and haven’t had to think about it. The weight penalty is marginal compared to the XLite 4.5 which is just 3oz.
If it’s in your budget the new pads NXT pads are even comfier.
You will notice a massive difference in comfort going from a sub 2 pad. I wouldn’t honestly consider anything less then a 4.
I've done this, woobie over an enlightened equipment quilt. Cuts out any drafts to the quilt and was toasty warm below the rated temp of the quilt despite my tendency to be cold.A Kifaru Woobie over the bag makes a tremendous difference. It also serves as a great way to stay warm when glassing. Keeps feet warm too.
and the doobie is even better.....