I’ve played a few hundred matches of 9x9 and a sad zero matches of 19x19. I’m pretty sure I’m not even close to beeing as strong a 19x19 player as on the smaller board. And there’s a few people with thousands of matches on a given boardsize but basically none on others.
I feel like it would be an improvement to use the ratings for the specific boardsize in ranked matches for the pairings, especially since they already exist. 
The latest tests for the rating system indicted that the overall rating is an better predictor for the outcome of a game than individual boardsize-speed ratings.
You can run your own analysis with the code: GitHub - online-go/goratings: This repository contains the (future) official rating and ranking system for online-go.com, as well as analysis code and data to develop that system and compare it to other reference systems.
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Maybe playing 19x19 will give you some good surprise, try it!
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