I'll throw some of that sunny weather in my case, (I'm coming home to the UK for crimbo) but wouldn't you rather have a white Christmas?
I'd like to use a little fill flash, the strong sun (sorry, don't mean to rub it in) here in Arizona sometimes causes faces to be underexposed if the sun is behind the subject. I wouldn't use it though because I don't want to disract the riders.
I have the canon 550 which when used in manual mode works great, like I said, I haven't used it at a trial yet.
So which lens did you go for?
Matt