Toto,
There comes a time when a larger throttle make little or no improvement to performance. The rest of the intake such as the head, plenum and intact tract limits the amount of flow. So a larger throttle body will not make any power gains. But with a larger throttle body, a 10% accelerator input which normally translates to a 10% throttle opening , will flow more air cos the opening is larger. the effect that you get is a better acceleration kick. But when you extend to 80% or so opening, the restrictions caused by the factors listed above will limit the flow and thus limit the produceable power. That's why forced induction cars make big big figures.
If your car has a limited throttle, then a larger opening will provide good results. An example is the previous Ford Focus, the 1.6L engine has a throttle body opening of about 50mm and is a major restriction.
If you wanna go upsize, a larger body of about 10% in dia is about the max that you should go to free up any possible restrictions and be within the manufacturers programing of the ECU.
Cheers