Haven't read the entire thread yet, but want to make a comment anyway.

To me, the missing piece of gear is a thin skull cap with material which drapes liberally down the back of the neck. I'm talking about the super thin cycling skull caps with the extra material being thin like the sun shirts you can buy.

I wear a skull cap every time I ride for two reasons: to get keep the pads clean-ish but mainly to keep my thinning scalp from being burnt through the vents of the helmet.

I can't think of anything that is more exposed at a direcct angle to the sun than the back of the neck. Why don't they make (or maybe they do?) a skull cap with back of the neck protection too? I've been thinking of cutting up an old hooded sun shirt for this.