The problem with boring out the throttle body is you do need a ventury with a wider diameter to properly seal. Additionally, the whole TB boring process is something useless unless the Intake Manifold-to-Throttle Body port is matched to the newly widened diamter of the throttle body port. As is in the case when a head and manifold aren't port matched, this creates "walls" effectively damming air and creating eddies within the plenum-- disrupting the objective laminar flow to the head. This (obviously) creates some rather strange flow patterns within the manifold plenum itself.
I have no idea if this would significantly change (for the worse) the results from a bored TB, but I do know that when porting an intake manifold, a manifold outlet port of wider diameter than the head inlet port produces this same effect, and the result is highly detrimental to improvement-- in cases such as these you might actually see worse performance over the unmodified manifold.
