Switched to the X-Therm large and couldn't ask for anything better. Plenty wide to lay on your back without your arms laying off the sides, horizontal baffles are comfortable and high R-value yet only weighs 20 oz. Not cheap but wait for REI's annual sale and pick one up for 20% off plus any dividends you have built up. Heard lots of complaints about noise but it really hasn't been an issue.
Another reason I went with the X-therm over the X-lite is because it has thicker material on the bottom (70d vs 30d) so hopefully it will be more resistant to any punctures.