Been using Colemak for 50 days now and slowly approaching my old QWERTY wpm of around 60-65 wpm. However the variance of my Colemak wpm does vary quite a bit ranging from 63 wpm which I just did on Amphetype, down to the mid 40s sometimes even on relatively easy text. The slow speeds seem to result from tiredness or trying to push it to the next level which is surely required to get faster even at the expense of some accuracy?
Then after a resting period or sleep and going back that speed I tried to attain before sometimes just magically happens without me even realizing and it's quite a nice feeling. Sometimes you are in the zone and your fingers are hitting all the right keys dead centre :).