Seolman, maybe have a look at this site
Freewriting Techniques as well. It is a technique called free writing, it is basically you need to write, or type your thoughts as fast you can not really going in any specific direction, with your thoughts but just writing. i have tried it once, and as i am a fairly quick type was writing an average of 70 words a minute for 28 minutes, this was just writing my thoughts, and i was quite surprised i only had one or two few seconds where i was lost as to what to write but it came back again.
Vangogh, maybe the slower writing on the blog posts, could be caused by that you are answering your own internal question or a question you have formed from others comments somewhere. Which is also something i have had some problems with. If i see a questions someone asks, i may modify it slightly but i can reply to it much easier then if i make my own question.