rx-8_or_?

When you switch to 19in wheels, you should make sure you buy lower aspect ratio tires so the diameter of the tires stays the same, and you don't have to recalibrate your speedo/odo-meters. If you do that, the big wheel could just end up adding to your unsprung weight, slowing down your acceleration minutely, and making your suspensions response slightly slower. With the shorter sidewalls, you should also see a reduction in sidewall flex which will translate to better cornering, and a harsher ride. That last statement will be true only if you fit the same brand/model tires.

Of course, if you keep the aspect ratio the same the quoted statement holds true. Remember that your diameter will increase, your speedo/odo meters will be off, and you should re-calibrate the speedo/odo.