Layering on one of those 15-denier nylon windshirts that weigh in at around 2.5 oz to 3 oz adds an amazing amount of warmth, but still lets me adjust ventilation a fair amount by unzipping or pulling up the sleeves.

Then again, I may have more tolerance for adjusting my warmth by putting stuff on or taking it off than you do. It doesn't bother me much to take off the pack for a minute, adjust my clothes and put the pack back on, as long as I don't need to do it so often it ruins my hiking rhythm.