IMHO if you skip 9 speed entirely the only thing you are missing out on is Dura Ace 7700 which is simply wonderful.
5500/5510 and 6500/6510 were OK, but I think 10 speed 5600/5700 and 6600/6700 were better groups with a higher quality shifting feel, especially on the downshift from the big ring to the small ring/s. 105 and Ultegra 9 speed had a very abrupt drop, slamming the FD to the limit screw. DA 7700 and the 10 speed groups handle that with more finesse.
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