My current setup is...
Wheels: 5-100 17x7.5 +42 72.6mm>54.1mm
Tires: Michelin Pilot Sport A/S 3 Ultra High Performance All-Season
Size: 225/45ZR17 91Y
On the next set of tires I plan to go 235/45-17 primarily so I correct the speedometer to match GPS units. If you ever did a test on stock tires you'll see that you are easily off by at least 4-5 MPH when cruising at 80. With my existing set of tires, I think I am still off by 1-2 MPH.
From personal experience, Lexus (as well as Acura) is very conservative in MPH readings as well as estimated gallons left in the tank (aka they think the driver is dumb and will lie to you). With my other car (Mercedes), the speedometer matches my GPS units EXACTLY as well as correctly representing the gas gauge in that 1 tick = 1 gallon. In this scenario, if they tell you, "you are out of gas", by turning on the low gas light they mean it!