Unless you do something RADICAL don't bother swapping in a set that wasn't made for your motor (i.e. 2.8 w/ 3.1 injectors). My car runs a lot smoother with the stock injectors, I can't smell gas from the exhaust like I could with the 3.1 injectors, and perhaps most impressively, my mpg went way up when I reinstalled my stock injectors. On the highway with the 3.1 injectors, I got just under 16 mpg, with my stock injectors I got ( drumroll please) 10mpg more, just under 26 mpg.

The only real mods to my engine are a powermax 2030, 1.52:1 roller rockers, and a cloyes timing chain.
Obviously this is a significant change, maybe not everybody would have this kind of difference in performance.

Make your own decisions, but I think this may answer a few questions

 

Injectors are rated according to how much power the engine puts out. Plus gm's seem to run a little on the rich side anyway.

n/a
(hp x .50) / (injector qty x .80) = lb rating you need.

boosted
(hp x .60) / (injectors qty x .80) = lb rating you need

 

the problem with putting in bigger injectors is the computer is calibrated for a certain size (the injector constant) which must be compensated for in the computer chip. i have heads and headers done and i ran out of injector. now i have 19# fords with a custom chip.