I have an Evoluent wireless on order for work (they were kind of pushing me to order something, I think to prove they're trying to do something about my condition). From my test drive it feels awfully big. I learned that I have quite large hands, and it just fits me, but it "drives" big, like you'd need to turn down the speed and use a lot of desk space to be precise, the mouse equivalent of a 1970s heavy duty truck gearshift.
The mouse I've been using since the pain got bad is the Microsoft Natural Wireless Laser Mouse 6000. It's the only retail mouse I found that doesn't pronate your hand much. (I was actually surprised and disappointed that there weren't more alternatives; have ergonomists just given up on the whole pronation thing?) Last week I went back to my old office where I'd dumped my previous Microsoft wireless mouse, which I used to love, and it felt SO uncomfortable -- the MS Natural 6000 has corrupted my sense of normal.
Anyway, if the Evoluent doesn't work for you, think about trying the MS Natural 6000. Like a good automotive gearshift knob, it feels more comfortable than it looks.