Man, I couldn't imagine how cold it would be without a pad. Sleeping bag ratings assume a pad and shelter to come up with their magic number.

I used the Z-lite for a few years, but am now a faithful convert to the Gossamer Gear NightLight torso pad. Warmer, more durable, and lighter.

Something else to consider is with a pad, you open yourself up to a new line of backpacks which use the pad as the stay. I roll up the NightLight and place it inside my MLD Prophet, it makes for an incredibly light and comfortable pack.
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