Simon T.:
Did you write about your story of your practice before reaching fourth path? I would like to know about it.
You can look at my practice journal on KFD. Towards the beginning, someone asked me a similar question, so I recounted the story from memory.
(If I had to characterize my own difficulties with attention, I would say that I strongly leaned towards the "speculative" phenotype described above.)
The most helpful method I used (getting me the first two paths very quickly) is here: http://kennethfolkdharma.wetpaint.com/thread/4647646/Drunken+Vipassana+Fist%3A+An+Introduction
Please note, I am explicitly telling you
not to try this with amphetamine or any prescription drug whatsoever. The method can be much more intense than my neutral writing style makes it seem. In combination with amphetamine or a prescription drug, you would be taking on great risk. However, you may find some useful ideas in my post which you might be able to apply, in a modified form, to your own case.
Simon T.:
Regarding "noting speed" you talked about in the other thread, I don't know yet. I never really managed to put well the noting into practice. I find that it obscure the object and it's not true awareness.
Have you taken something as simple as your visual field as an object to note? For example, staring at a wall, or a large or small kasina, or the visual field as a whole, and repeatedly noting "seeing...seeing..." during each individual moment that you notice that you are seeing the kasina or visual field? This is very simple, and the visual field is generally much more distinctive and clear than the motion of the abdomen (the traditional anchor of the noting technique)
If you found that this was doable, you could move on to varying your noting speed in order to see if you could find a speed that keeps your attention grounded in the process of meditation and away from discursive thinking.
You could try different kasinas or different sensory modalities as well, if you were not satisfied with the results at this point.
This is what I had in mind by experimentation; take the bones of one technique, figure out how to make it work "well enough", and then keep varying the details and implementation until you get something that suits the idiosyncrasies of your mind especially well.
Keep in mind that rapidly noting "seeing" is one means of attending to the impermanence characteristic of sensory experience, and recognizing this thoroughly enough is sufficient to attain stream entry.
Monks, eye-contact is inconstant, changeable, alterable. Ear-contact... Nose-contact... Tongue-contact... Body-contact... Intellect-contact is inconstant, changeable, alterable.
One who knows and sees that these phenomena are this way is called a stream-enterer, steadfast, never again destined for states of woe, headed for self-awakening.
http://www.accesstoinsight.org/tipitaka/sn/sn25/sn25.004.than.html
EDIT: Not being a Pali scholar, I am not sure whether the meaning I intended is better conveyed by this one instead: http://www.accesstoinsight.org/tipitaka/sn/sn25/sn25.003.than.html