I just got my Shamu back from MacEntyre with his end channel mod and had a chance to try it out yesterday with the temps in the 30s. I was dressed in a wool beanie, poly tee-shirt, long sleeved lightweight fleece shirt, medium weight fleece jacket, long pants, and heavy weight wool socks. No TQ because I wanted to test just the UQ.
The Shamu's channels, with their braided cord pulls, were very easy to draw snug and closed up the ends nicely--something I could never do without the end channels. At 38*F and with 20 mph wind gusts, I was very comfortable and warm--no sign of CBS.
Later, I added a single IX layer to bring the Shamu up to 3 layers of IX, and at 31*F, I was just as comfortable as with the 2 layers at 38*F. I'll bet that with the 3 layers and a TQ, I could easily dip down into the 20s. At 12 oz, including stuff sack, the Shamu IX UQ with the end channel mods, has a terrific weight-to-warmth ratio and will be my 3 season UQ.
The Shamu is finally living up to its potential... Thanks MacEntyre... Happy New Year!