The advantages of EFI are numerous, but primarily relate to drivability, not performance. Better fuel milage, easier starting, less problems with vapor lock, less harmful emissions, etc, etc. I'd note too, that a switch to an EEC-IV system means you are not only using a computer to control the fuel injection system...the computer controls ignition timing as well. An EFI system is vastly superior to the carburetors in about every way. That's why Ford started putting fuel injection on Mustangs in 1986.
The downside to the system shown (and the one I'm working on) is the look. I'm not a big fan of the "look" of the 5.0 fuel injection system under a vintage mustang's hood. There are other systems out there that will give you some of the benefits of EFI without sacraficing a mostly vintage appearance, but I've decided not to go that way (Mass Flo EFI for example) due to the cost.
If you are interested in this, I would HIGHLY RECOMMEND purchasing the late Charles O. Probst's book "How to Understand, Service, and Modify Ford Fuel Injections & Electronic Engine Control" specifically his second book covering 1988-1993, which concentrates on MAF systems...which are superior to the earlier speed density systems. This book is available (again) from Bentley Publishers. People were selling used ones on Amazon a while back for $70 or more. I got mine brand new from the publisher for the list of $29.95, after they came back into print.
Just beware that once you read up on all that EEC-IV can do for your car...you may find yourself searching all over the internet for parts. That's where I am now.
I enjoy my EFI, but I think you should do it because you would enjoy the challenge, or what ever personal reason, rather than because of any precieved advantages. You'd have to do a lot of driving to recoup the money spent on EFI. Do it because you just want to, rather than because you feel a need. If I'm making any sense..Hehheh