More from the 75-300 'New' cheap-o

Thanks for the "insta guide".  I've got a BBC and two "New"s waiting to be tried out on the A77 that I just got.  I will take one of them to a college football game next weekend, but I need to figure out how to get them micro adjusted on the A77 first.  Does one perform the back focus test with the lens at 300mm or at 75mm?  I realize the A77 will not know the difference between the two "New" lenses, but what about between the BBC and the New?

Thanks,

Andy