I have a 7D and I want an UWA lens for motocross to give a different perspective. I don't always plan on having a crop frame camera as my primary (will possibly buy a 6D in the future at least). I was wondering if anyone has had any experience with the 10-22mm f3.5-4.5 USM in dusty conditions? Will it stand up to that type of work or would I be better buying a 17-40mm f4 L instead and just put up with the fact I'll only get about 25mm at the widest on the 7D? Any advice on this would be much appreciated or if anyone has any pics taken with the 17-40 on a 7D that you could show as an example it would be great to see a couple at 17mm. Thanks in advance!