I think it all has to depend on what suspension your running! I've seen plenty of xB2's with 20's but they aren't lowered. All the ones that I've seen lowered with 20's have rubbing issues.

More info would be nice

With that small of a drop, some people have gotten away with the 20x8 wheels (which there isn't many wheels available in that size) but that also includes them putting on very low profile rubbers! They still rub sometimes.....just not as much! I wanted the biggest wheel possible and the most drop possible with no rubbing. I researched a lot too. I went with the Tanabe DF210's and a 19"x8" wheels with a 45 offset and with a 225/35 rubber and my research payed off. Haven't rubbed once even with a loaded car (Wife, 2 kids, myself and a complete audio system in the back).

Hope this helps! Maybe someone else can chime in with more info.