Okay, I'm back again with more long term results, for those interested.
Ektachrome E100-anything does not appear to be well suited for low light pinhole work with the Zero Image in 25 or 50 mm setup. I think it would be difficult to work with this film on those Zero Image 120 Roll film cameras too. The vignetting is highly exaggerated with the Ektachrome to the point you will lose about half your surface area or more due to blackout vignetting. A lot of the kinds of compositions one would use with ultra wide angle pinhole make for naturally darker regions anyway under most lighting conditions. There seems to be an extra curve for Ektachrome, particularly in dark regions of blues and browns, reds, yellows. Greens seem to pop up above the rest, or maybe it's because it's unusually green this year in California.
Second thing to take note of, Ektachrome does in fact have a reciprocity effect and it is mighty steep once it begins. I haven't yet found the sweet spot but I doubt that you can use the approach Kodak supplies on their fact sheet. That, in my opinion, could only apply to lensed environments because I actually attempted to use their figures this past weekend and man they are so off! I have to go reshoot half of these 18 I just developed, if I want those shots. Oh, I probably will too, now that I know what I know, I'm going to treat low light situations like in a Redwood grove with a gushing stream waterfalling all over the place just a wee bit different.
I could rewind the figures and find out what factor was applied to get the figures that Pinhole Designer has for TMax100, but I might blow a circuit with that kind of math. Anyhow, when TMax100 is 5 seconds, Ektachrome seems to be 4 seconds. When TMax100 is 30 seconds, Ektachrome seems to be about 15 seconds. When TMax100 is 1 minute this is where I am failing big time. I know that 1 minute it way too overexposed because I have a few slides that scream loudly because of blocking in the sky and complete lack of blue in that region. The trouble I'm finding is finding the right place to draw this curve. But I will continue to report my findings. Believe me there will be findings because I'm shooting a heck of a lot of film these days. And I have a lot in the freezer still and know where to get a lot more for the same low price (how does $1.75 a sheet sound on Readyload 4x5's? )