Appreciation post: the retired guy at the REI in Boise who spent 25 minutes with me on sleeping pad R-values
He pulled three pads off the shelf, had me lie on each one right there on the floor, then said "the $40 one will keep you warm to about 30 degrees, past that you're paying for the extra digit" and it stuck with me more than any spec chart ever has, so now I'm curious what random in-store advice actually held up for you folks on real trips.
Close, but the temp rating on pads is about comfort, not safety. A $40 pad at 25 degrees is cold and sucks, but you won't freeze like you would with a bad sleeping bag rating. The guy was right about the price jump though, that extra digit mostly buys you less shivering.