What sort of power can I expect from porting out my intake in throttle body?

It depends on how well and how much porting is done, polishing it afterwards plus the porting would be better also., but match porting and polishing is a good thing.

w/o any engine top-end mods... roughly 5 to 6 HP. But you'll get noticably better throttle response. If you're doing it yourself, go for it... But I'd wait until you do a h/c swap w/LS6 intake... or something along those lines.

IMHO.... :)