Awesome flex!!!
The bump should start contacting with about 1" of shock shaft remaining, but it depends how soft the bumps are and how much they compress under load. You'd almost have to remove the coils and bottom it out to see when the shocks bottom out, and then put in the bumps to see how much they compress under the full weight of the vehicle to try and get a baseline. All of that isn't quick to do though.
Thanks Mike, that helps. I have a pair of your guys Timbren bump stops that i'll be fabricating a mount for so I'll shoot for contact with 1" of shock travel remaining and see where that gets me. I appreciate it!