im about to order the Sigma 18-35mm f1.8 + a focal reducer to go with it. because of the budget i'll go with one of the cheaper focal reducers from ebay, because from the tests i've seen they deliver comparable results to the Speed Booster.   since these focal reducers are available for pretty much all mounts, including canon EF, is there any reason i should go with a Nikon mount anyway? its the only option for speed boosters because those dont come in an EF flavor, but many of my colleagues h