Stem length: going shorter from 90mm.... 80mm or 70mm?
I would go with 20mm difference. It is enough that you will notice it, but not too drastic. If you like it but it is just too much, then go to 10mm, but if you start with 10 you may not feel what it is doing differently, though when it comes to really fine tuning, 10mm is does make a slight difference.
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