thanks for this post. There are a lot of things you can try to implement to get your speed up. I use to practice like this for many years, but recently i've started to implement a lot of different approaches, like playing really really slowly whole notes at 60bmp and building up the speed from there. this is the speed that can help you be totally aware of your whole body and the tensions. usually what happens with faster speeds is that you start to build up tension in your arm and it's therefor impossible to progress fast. once u're able to relax your speed usually goes up. but in order to stay relaxed you have to start slowly. i've never practiced so slow in my life but now that i do this, my playing is actually transforming in front of my eyes.
i can write some more on different strategies for building speed if anyone is interested.