Here are the facts. The stock 4.3/5.0/5.7 tbi casting flows 520cfm stock. The injectors can be swapped, and we have clients running 12.0's with TBI in 4wd trucks, with 35 inch tyres-this indicated how much fuel can be delivered, which is more than the casting can flow air.
TBI systems are with these main limitations:
Little or no tolerance for lopy idle.
Roughly 5000rpm limited system, though some go higher, but this works out well, as smooth cams in the right motor run well to 5000rpm.
We have a 383/350hp package that we have design, that makes 425+# of torque, and it peaks right at 5000rpm.
Holley tbi units cannot be perrfectly tuned, because the injector slope, or response to controls is too far off from the factory injector behavior pattern, and the old tbi ecm's did not have elaborate programming like some newer systems do to compensate for differently behaving injectors. HOLLEY TBI'S ARE EXTREMELY UNRELIABLE, PERIOD.
EFI systems use 3 dimensional timing curves, and will typically earn 2 more+ mpg, and give you 30-60 more # torque in the lower rpm ranges (1000-2500) than centrifugal advance, found in distributors, not to mention when it's tuned right, just plain faster. 454 TBI units flow around 650cfm, if you need more but rarely you do.
If you really want your mind blown, then I'll also tell you that you could, if you wanted to, but only with qualified EFI design engineering, you could run a carb, with the EFI 3D timing controls for just that purpose.
In short, exactlywhat you want to do needs to defined, and a qualified EFI firm needs to be consulted about the feasability. Unfortunately, such firms are few in existence, but as you may know by now, I might be able to help you decide which is best for you. Hope this little bit of info helps.