The step-downs to 77mm work great, until you buy the 16-35 (which I just did), which is 82mm - so now I would have to buy all the filters in 82mm.
Also - I frequently rent some of the larger telephoto formats, like the 400mm, 600mm, etc...
Screw-in filters are good option - but matte-box with trays is the way to go forward, if You are serious about building your own filter bank...
Peter



