the fast efi system is good. for your size of an engine you can use a large throttle body.

in a carb because of the venturi effect of drawing in fuel, you have to limit the cfm so you get good atomization and a strong signal to pull fuel from the bowls.

in efi you don't have to worry about this as the injectors will atomize the fuel and deliver the proper amount not matter what cfm your throttle body is.

in terms of cfm:
1. small cfm will limit horsepower and give really good throttle response
2. too large of cfm will not add any more hp than your engine can put out, but part throttle drivability may suffer as well as fuel mileage.
3. the just right zone. good throttle response, just enough cfm to not limit hp, with tuning can achieve decent mileage.

yes on fuel injected engine, the injector size is more critical than throttle body cfm. to large of injectors, and your low rpm will suffer, as well as driveability. too small and you lose hp and can run lean.