I've used Boure's knicker in 90 degree Tucson sun ( http://www.boure.com/2653.html ). They're a lighter weight (and, for people with long legs, longer than most knickers). I can't say that I was happily comfortable, but it was "OK".

I was also wearing Boure's SPF jersey. I think I was hotter on top than bottom--which surprised me because I thought all that black would be too much. Like you, I can't be in strong sun multiple days in a row, for now, I can get away with just covering up every other day. Knickers, long-sleeved jersey and cool max buff for the head, ears, and neck. I try to pick the cooler of consecutive days, but that doesn't always work.

DH used my arm coolers ( http://www.teamestrogen.com/products.asp?pID=20747 ) and swore that his arms were more comfortable than his shoulders. I keep waiting for someone to make leg coolers.