Note: Stock Svt Throttle body is 63mm.
Stock SVT exhaust is 2.28"
Ok Your throttle responce will be greatly improved! the 2-4mm increase in bore, It has not proven or disproven to gain or stay the same in power. If your engine is Forced induction then you will see a better power gain with a larger throttle body.
Another option is porting your stock SVT throttle body. Some say they have the same gains as a 65-67mm tb. but I dont trust doing that kinda stuff myself.
In the end It makes your car that much funner to drive, and you get from 0-60 a little faster.
2003 Sonic Blue SVT Focus #524