I have a Rev X 20 as well and for temp regulation I just stick my leg/foot out of the side. You won't always have the option of changing your pad and throwing extra clothing in the middle of the night generally is a circus act, but you can always relatively easily expose another leg/arm etc to cool off.
Everyone is different but, being from mild Southern California, I've found that 20 degrees puts me solidly in the "holy hell it's cold" factor, so because I know what I'm in for, I have a puffy and capiline bottoms on. For me, temp regulation gets more finicky in the 30-50 range, that's where my feet go in and out of the quilt throughout the night.
Once you've experimented a bit with the quilt in a variety of conditions, you'll know what pieces of kit to bring to augment it.
Hope that helps.