OK well it depends on what foam pads you're also carrying, but probably won't need all of that (although warmth would almost certainly be guaranteed!). A Z-lite, however, is about as compact as (or "least bulky") one can get and still have adequate insulation. For me, a GG Thinlight did not offer any appreciable benefit and that the R 3.3 rating of an Xlite is exceedingly generous.
I have an Xtherm Max (R 5.7, 20.6 oz) and when it gets down to about 15°F or lower I still need to supplement it with my long-ish 3/8" Evazote sit pad in the torso area, especially when camping on snow.
Definitely test various combos at a campsite not far from a trailhead before getting too deep into the woods.