I have always seen it as the Arc of Great Shifting.
Revelations 193.9 says:
'Those that have fitted too small a length of cable outer for the rear mech shall forever experience undue tightness in their power of shifting on the bottom cog - the path to ultimate shifting is an arc of exact length, great smoothness and inner lubrication'. Amen.
If the stop screw is correctly adjusted and it works in the two outer chainrings then it's probably the b-tension screw needs adjusting. The top jockey wheel is offset from the cage pivot on the derailleur, when you drop to the small ring the cage pivots backwards and the jockey wheel upwards, if the gap is too small the cassette teeth touch the jockey teeth through the chain and make it feel jumpy and horrible. A couple of turns on the b screw should sort it.
Or the chain could be slightly too long, which again means the cage is pivoted back further than it should be and the jockey is too close to the sprocket.
Could also be neither of those and something else already mentioned but worth a look.
Off-topic sorry, but out of interest are the Dura Ace mechs actually any different up to 10-speed? I've used 7800 and 7900 rear mechs on 9-speed MTBs and I'm pretty sure they're the same as all the rest! From memory one of the front mechs was definitely specific to the Dura Ace front shifter though.