As far as I know, and hopefully someone can chime in here if I'm wrong (which seems to be a theme these days, lol); the 6112 is as "high-end" as one can get, in terms of shock diameter, oil volume, and sheer girth of housing, while still retaining the rubber upper pillow ball mount.
Anything chunkier has a spherical bearing at the top that gets all squeaky all the time, and people can generally grow to hate easily. But slamming a truck off dunes and rocks obliterates the pillow ball and allows the shock to have some play, killing the shock.
So, one takes the good with the bad...
If I recall, the 6112s and 5160s are rebuildable, so the valving could be changed to match driving habits and spring rates (obviously by an authorized Bilstein dealer that understands how to design shock valving). And of course, if you wore them out you could just have them rebuilt for less than a new set... if you can stand the downtime.
The 6112 and 5160 combo isn't the best bang for the buck... but I think they're the most bang for a daily driver: the only downside to them is cost, as they have all the features needed for light/medium use.
I did alot of reading and highway/winter use and the spherical bearings on high-end shocks are not a great combo... and every squeak drives me CRAZY! So I wanted the OEM style upper pillow ball.
Hope that helps.