Have you tried testing at say 10kms and then at 20kms and finally 37kms comparing bandwidth, this eliminates any radio card issues and location, You mentioned a clean frequency usage scan but be aware the scan only displays frequency usage by 802… compliant gear and not the non compliant stuff, spectrum analyzer is the only way to know how crowded the band at the location really is.
It maybe a tx vs rx issue at both ends, where the tx is swamping the incoming signal, by reducing the data rate increased the tx power power, R5h goes from 20 to 24db @24, hence your ccq went from 80+ to 90+,
I am a little confused then did you conduct the reading at 24 or 54 when your posted vert receive @ 13/ vert send 13…etc?
I am using XR5’s and find them good,in actual fact all my PTP + Ap’s use XR5’s and all of the cpe’s use UB5, i don’t use mikrotik cards,
R5h = @54 = 20db
XR5 = @54 = 23db
ack timeout i use nstreame with dynamic, check
http://forum.mikrotik.com/t/ack-timeout-script/34102/1
n21roadie