So I've been contemplating switching to Colemak for a while now, and finally made the plunge yesterday. I was mostly convinced by some of the comparisons on the Hi-Games tests as well as this website: http://patorjk.com/keyboard-layout-analyzer/ . I have chosen to do a mostly cold turkey approach, but with a bit of practice each day in QWERTY (about 10-15 minutes worth), in order to hopefully mitigate speed loss.
My QWERTY typing speed is around 75 words per minute (based on the average of a 2 minute and 5 minute typing test on Hi-Games, I average around 80-85 in burst typing tests, such as Typeracer.) Luckily, it hasn't suffered at all yet from learning Colemak. Interestingly, I almost feel more precise, probably from being forced to practice Colemak so slowly.
So far I haven't tested my Colemak speed in any timed tests, but based on TypeFu and Typeracer, my average seems to be 35-40 WPM.
I enjoy using this layout a lot already, but I have had some mental blocks with certain keys, most notably J and K, and to lesser extents, U and F. I'm sure this will come with more practice.
I also love the use of the cap-locks key as a backspace, it feels like a huge time/strain saver.
I'll post some updates with my speed as it comes along.
P.S. This message was typed in Colemak!