OK, so I know ~ 40 horsepower, but beyond that, I cannot figure out much more of a difference? Is the Supersport a trim-level that has the same motor, but just a different tune than the "regular ol' " supercharged version? I currently have a 2011 XJ L Supercharged but am looking for another one so that one can be a parts donor for the other. I have an opportunity on a SuperSport of the same year, but my research has pulled up nothing of note when it comes to differences. Best I can find is that it is just tuned to XKR spec, but same everything really.

The Supercharged means only on engine (3.0 SC or 5.0 SC), its not a trim level. Supersport is a trimlevel. (available even with Diesel engine)

Here is the 2019 brisure as the 2011 was the same. SuperSport had every option except rear seat entertainment screens. Also the SuperSport had 510hp.

My 2013 SuperSport has the rear entertainment screens, but not sure if that was an option in the earlier years.

Mine 2010 SS LWB had a RSE screens.
Basically SS is 510hp AJ133SC with most of the available options present inside of the vehicle. Somwhere in 2014 SS was replaced with XJR and later was re-introduced as a trim level, but that have nothing in common with the original SS meaning.

in 2013 they added the rear entertainment as standard equipment and made the advanced cruise control the option. Also the "standard" V8 was 470hp. The SuperSport was the first model in the US that has 510ph.and that was the max power in the XJ until the XJR.

Just a reminder , either you have a base 470hp SC 5.0 or top of the line XJR575, hardware is identical and we can easily make your 470hp car go over 600hp with remap alone on the 5.0 SC engines 😆

This is exactly what I figured but wanted to be sure. In any event, I ended up getting another 2012 XJL SC fully loaded from the auction. 80k miles. $1600. The one I already have will become this one's parts donor in the future, if ever needed.

Just an FYI in 2013 the electronics in the XJ changed from Denso To Bosch,