2006 Gs300 Awd 19"-20" Wheel Upgrade?

[nardeezy]

My wife and I bought the GS300 vehicle as a third car (newborn). We chose the AWD for safety, we don't live in an extreme winter area. I'm not fond of the stock 17" rollers. I went on www.tirerack.com and the largest recommended wheel upgrade is 19", why is that? It seems that the AWD chassis spec is .5" higher from the ground than the RWD. On the Tire Rack site a 20" upgrade seems to be acceptable for the RWD. I'd like to upgrade the appearance of my GS to look more sporty but not lose performance. Ideally, a wheel upgrade and if possible a minor suspension modification (lowered). I have yet to find a manufacturer that supplies lowering springs for the AWD. If any of you have any useful information please reply. Pictires would be nice too.