interesting. seems no real need to get the 50T.
20:40=12.78 20:50=10.22
22:40=14.05 22:50=11.24
the 22:40 is ridable. 20:40 maybe. the 50's prolly not.
so deore sgs RD-M592 will set me back $30, and the sunrace 9spd 11-40 will be $15. i can use my microshift indexed shifters, and the current crank maybe. it's 22-32-44...will have to check if the 44 big ring will exceed capacity. maybe switch that to a 40.