The differential/"heavy duty" horse has been beat dead in
this thread. The consensus is that it has the same or slightly improved 8.2" diff as the current 5th gen 4Runner and GX460, while the GX550 and LC300/LX600/Sequoia have the same 9.5" diffs as the LC200.
This kind of removed the LC250 from future consideration for me (though I have so much time and $$ invested in my GX470 that I intend to hold on to it for 5+ years anyway). I personally don't see the LC250 being a material improvement over the very proven GX460 (outside of fuel economy) while having less power and drivetrain robustness than a GX550. The GX550 is, on paper, is a pretty big improvement in capability over a GX460.
However I probably would pick a LC250 over a 5th gen 4Runner, just to avoid the under-powered 1GR and pick up a few more MPG.