Hi Molte,
I can't remember if I mentioned this earlier, but DD-X at a 1+9 dilution is not very dilute - it's just half as strong as the recommended dilution, so by analogy think D-76 (ID-11) at 1+1 versus 1+0. Typically when people resort to stand/semi-stand/extreme minimal whatever, developers are relatively highly diluted. With normal agitation DD-X 1+9 will probably develop Delta 100 normally in roughly 12 minutes (and including a pre-wash will accelerate this further), so if you're going to give much longer development times (even with no agitation) you need a significantly more dilute DD-X. It's also worth noting DD-X might not be the best candidate for that type of processing. The "theory" (usually incorrect but that's another matter) of long development times with reduced agitation is typically for developers that begin with a non-solvent formulation (low concentrations of developing agent(s) and sulfite, relatively high alkalinity with weak buffering).
On the subject of speeds, when people refer to alleged speed increases/decreases they should really refer to them as Exposure Indexes. Nobody is getting anywhere near ISO 200 from an ISO 100 film.
Regarding two-solution/divided development, below are some curves. Some of it is for Stoeckler's two-bath (which was one of the first of these) but the D-23 version(s) including Thornton are only trivially different. Some general results:
-Full emulsion speed (ISO or "box") is reached
-pH and concentration of second bath is largely irrelevant in the context of macro-sensitometry, borax being as effective as metaborate. Carbonate can increase emulsion speed very slightly but also increases fog
-Since the first bath is a fully functioning developer, development time in the first bath is how you control contrast
-Divided development tends to straighten the characteristic curve, and shortens the toe/shoulder
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