XTOL: calculating high dilutions (1+5 or more)

[farpointer]

I'm familiar with the older Kodak datasheets that list times for XTOL at 1+2 and 1+3. Anchell and Troop recommend XTOL at 1+5 or more for some scenarios, like technical films; does anyone have experience and/or references for starting points to calculate times for those higher dilutions?

I'll be using distilled water, and the FDC also recommends considering additional DTPA for those highest dilutions...