This is my typing speed chart on http://keybr.com, from when I started learning Colemak in June last year (x-scale is per test, not chronologically). I'd say my average typing speed is in the 50s with peaks to 80s.
The purple line is the "abstract score", basically how many mistakes you made. The peak is when I started using "sudden death mode", where I restarted the test every time I made a mistake. It allowed me to practice words a bit like piano phrases, but it was too tedious so I stopped.
This is also all done with the TextBlade layer layout (via Karabiner), but of course keybr doesn't test symbols and cursoring.
I have a chart for qwerty too but it is not very useful because I was practicing symbols (on qwerty) and my chart is all over the place. It looks like I'm at the same speed as with qwerty now, but I seem to remember being more accurate.
Here are my most errored keys:
As you can see, the ones at the extremes of reach have the most mistakes.
So my expectation is that with the TB I will first make more mistakes due to overshoots, and as I learn the size I will hit the keys that I want to hit more often and thus my accuracy and speed will increase quickly.
Interestingly, here is a heatmap of the keys I typed:
Compare with qwerty and you see that qwerty favors the top row:
