A 20 mph headwind really is brutal! Another way of looking at the numbers: my usual level speed in still air is around 12 mph. Into a 20 mph headwind, the same power output would have me going about 3.2 mph! I have plenty low gears but that is actually running off my low end. My lowest gear at my steady cadence is about 4.7 mph. At 3.2 mph my legs are slowing down quite a bit - not quite at the death struggle stage but getting there!