A good night's sleep is definitely a concern, but so are a few extra ounces on a 45 mile day. There's a trade off either way I go, and I'm trying to pinpoint the best compromise.
I've used a POE Ether Thermo 6 for most of my backpacking adventures, but recently bought a torso length Ridgerest and have used it for 3 nights so far. I'm plenty comfortable on that, and it's 9 oz, so I think I can go lighter and thinner. I've taken long naps on my lawn plenty of times and have slept directly on living room floors more time than I can count without any trouble.
It's worth the $10 to experiment with using a ThinLight pad on a couple of quick overnights, but I'd rather not spend $20 trying out both the 1/8" and 1/4" versions. I'd love to go with the 1/8" version, but if no one here has been able to get a good night's sleep on it, then it's probably safer to go with the 1/4". I do feel like at least one person has mentioned using the 1/8" as their primary pad on some ultra hike, though.