To lower or not to lower???

I have not had one at stock height for any longer than an hour after I buy them so I never put much thought into the overall travel.
Interesting about your upper bump stop, I guess it would depend on the clocking of the torsion bar if it could fall off the adjuster bolt.

It does depend on the clocking of the torsion bar. The problem with really large torsion bars is that the static weight of the car doesn't compress the suspension very much, so the ride height of the car is more sensitive to the actual clocking of the bars.

You can actually change how the LCA's are clocked on the torsion bars too. Typically you install the LCA's on the bars with them hanging down as far as they will go. But you can also install them one hex flat up from that, which results in the LCA's being pretty close to ride height. With the clocking on my 1.12" bars I found that there was only one way to install them, and to get as low as I wanted I needed to raise the upper bumpstops because the adjusters would unload at full extension. Not enough for the adjuster bolt to fall out of the LCA tab, but enough that I wasn't comfortable with it. If you look at the bumpstops that Hotchkis provides with their UCA's you can see they're taller than stock. I run the same ones on my car.

My next modification is installing tubular LCA's from QA1. That will do two things, one is that because the profile of the tubular LCA is shorter, I will gain back some suspension travel, about 1". The other is that because the LCA's are narrower as well I should be able to clock them differently than the stock arms. Although that may or may not work for my ride height, we well see.

Also, a 1.5 inch reduction in ride height as measured, say, at the wheel openings or at the K, does not translate to 1.5 inches at the bumpstop.
Aggressive cornering at a lowered ride height, even with 1.03s puts my S on the stops, which actually isn't bad.
It's hitting speed bumps too fast that spits the stockers open, and is really harsh with polyurethanes. I quit doing that.

Good point! The actual wheel travel is different than the travel at the LCA where the bumpstop hits the frame because of the length of the LCA between the bumpstop and the ball joint.

Even with only about 1" from my bumpstops to the frame (maybe a smidge less) I rarely ever hit the bumpstops with the 1.12" bars. Occasionally with large pot holes etc it does happen. That should also be eliminated with the extra space I get with the tubular LCA's.