Could anyone tell me if they think the Canon EF-S 15-85 f3.5-5.6 IS USM is worth the extra money over the Canon EF-S 17-85 f4-5.6 IS USM because I have just purchased th 7D and need a lens also I have been offered a very good condition Canon EF 70-200mm f2.8L IS USM II which a friend has been using but I'm not sure if it is worth £800 even though it is in mint condition. thanks everyone.