d) Currently using ID-11 with consistent results, but sharpness and detail mean something
when I go 16x20 and larger enlargements.
Would negs be sharper than in say Rodinal, D-76 ?...
Perceptol is the Ilford version or Microdol X, which was designed for fine grain, but will degrade apparent sharpness as it works by reducing gain leaving the grain edges jagged. By diluting to 1:1 or even 1:3 you get a shaper image. Apparent sharpness is not the some thing as how well a film resolves detail which is backed into the film. Rodinal will be sharper as any other high acutance developer. D76 1:2 may be shaper.
So it come down grain or sharpness. If you have read Berry Thornton's Edge of Darkness you want to find a copy, he goes into detail.
Do you get the rated speed of 100ASA?
In my experience with Microdol X I rate film at 1/2 box speed.
I don't have any experience with Delta 100, but have used Tmax 100, I don't often enlarge beyond 11X14, and Tmax 100 is more than enough for 11X14, a 16X20 in D79 or HC 110 should work just as well. Over the years I have moved from extream detail and grain to tone, I currently use Foma 200 rated at 100 and developed in MCM 100. But my next purchase will be HP5, want a faster film for 4X5, want to keep my shutter speed up at F22 or 32.
BTW, if want to use Perceptol you may to check with Freestyle, they carry a house version of Microdol X for a lot less than Perceptol.