The Neo Airs are the gold standard among UL backpacker's (and pack size is highly correlated with weight) - go with the X-Therm if you are worried about it, but I'd personally choose the 3/4 length X-Lite for that trip - it's about the size of a beer can with R of 3.2. Assuming same high/low temps, the ground in the fall will considerably warmer than ground in the spring. I tend to find a bag can make up for the pad somewhat, and for me, side sleeping relies more on bag, while back relies more on pad.