I don't run KO Propo anymore but I had really good luck with the Dasmikro Rx's, they used lower quality components which are similar to the Rx's made for FlySky and I measured frame rates in the 12ms range IIRC, they were very reliable and not a single one ever failed on me over the 2+ years experience I had with the EX-1 before switching brands of transmitter:
https://www.banggood.com/4-CH-Receiv...-p-944937.html

It uses the same pin-out as the KR-212