I doubt that you would see any real gains just by changing the throttle body, think of the restriction of air through the filter, the turbulance caused by the flexi part of the intake pipe, the coarse casting of the plenum & lower intake manifold, & then the size of the intake valves, their lift height & cam duration. Then there is the exhaust side.
So are you really going to achieve anything by solely changing the throttle body. No, save your money for some more petrol & tyres