Great post Randy! You obviously put in a lot of time into the experiment and original post. Well done!
That is a very respectable 100 yd grouping with the crossbow....not quite sub-moa though.
You mentioned that you started to get good groups at 100 yds and I have to ask.....How many groups did you shoot before you took the picture of the one that you posted? I don't know what your string looked like before you started shooting but by the looks of it in the close up photo it looks like you did a fair amount.
This summer I'm definitely going to have to try the 100 yd shoot with my Excalibur Exomax to see what results I get. I have it sighted for 30 yds which is a suitable distance for the type of hunting that I do.....in the woods from a treestand. My groupings at 30 yds, prone offhand, are similar to your 100 yd grouping so I'd be interested to see the results. I'm pretty sure that once I'm set up I can find a rifle shooter out at the lake who's never shot a crossbow to test that theory as well.