I used to have a pair of Serengeti's. I really liked them until they broke and I got a pair of Rx Oakleys. Minutes with the Iridium Gold lenses. Second pair is the A wire with Rx. I LOVE these things. The iridium lenses cut the glare like no other pair of sunglasses I have ever worn. they are NOT cheap. 200$ for the glasses and 200$+ for the Rx, but I swear by them.
I thought the Serengetis were good until I tried the Oakleys.
Those of you that are IFR rated will understand about when you are climbing though an OVC layer and it starts to get bright then POOF you're in the clear. The sudden glare of sunshine was not an issue, and when you're in that 'bright' IMC, there is no glare, no pain, and lots of sharpness and clarity.
And riding my little Rebel home and its getting towards sunset and the sun is right on top of the mountains and right in my eyes, I can still see.