FYI here's a XK with 4" superlift and 285/70/17 (which are basically the same size as 295/55/20): http://www.jeepcommander.com/forums/...ad.php?t=10817
Here's another: http://www.jeepcommander.com/forums/...ad.php?t=10455
^Those wheels are 8" wide with 4.5" backsapce.
Based on those vehicles, i think 295/55/20 would be a good option if you wanted to run the 20s. And the 20x8.5 w/+10mm offset would put the stance VERY close to that second one I posted. Your tires would stick out just a hair less... but the increase from 285 to 295 wide on the tire would probably make up for that, so they'd be identical to the naked eye.