I have three NR derailleurs working with 28t cogs. Patent 72, 74 and 80. As mentioned, it takes chain length fiddling and dropout position fiddling. Also, big front-big rear is strongly advised against on all three of mine. Shifting is actually pretty good with new 6/7/8 speed chains and good freewheels, with the Shimano Z012 14-28 it is particulary good. In setting up one of them, it seemed that the derailleur cage had a strong desire to introduce itself to the spokes (stand testing only). So I gave in and put a spoke guard on it and very carefully adjusted the derailleur stop. Seemed to be the worst when there was enough chain to handle the big-big cross chaining.