One might expect people with strong Si to be much more interested in knowing things for the sake of knowing it, but I find it's the introverted intuitive types who seem to be most interested in in an idea or a fact simply for the pleasure it brings. How would you describe that process of taking in and cataloging all that data? Is it largely automatic and unconscious? If it's conscious, is it completely neutral, mechanical?
I don't know if I'm quite ready to acquit Si for it's role in the ESTJ's force of will just yet though ;-) You are correct that it's more precise to point out that the action part of that archetype is Te; Si is only responsible for the warehousing. I have had conversations with ESTJ's about painful past experiences, however, and I was struck by how nakedly painful it was to revisit those memories. The familiarity, I think, is key. I can see how a determined Te being multiplied by the visceral immediacy of Si would give the ESTJ more spit and vinegar than the average person.
Mind you, I'm also relying a bit on some logical leaps, perhaps. I find it really pretty easy to forgive past hurts, and I don't spend really any time dwelling on the past. 8th position Si has got to be good for something. lol
Have you done much with shadow functions and projection? I know how an ESTJ's 7th function Ni came across to me, a Ni dom. I'd be curious to hear from you (or any other ESTJ) what 8th position Si provokes in you as a reaction.