I have not done a back to back with the FI Tech but I've done back to back with the Holley EFI setup. No real power difference between carb and EFI but EFI allows you to "find" power much quicker. It can take a long time to figure out the correct jetting and ignition tune for an engine with a carb and distributor but EFI allows you to very quickly test different tunes.

On the dyno we are able to test a bunch of tunes in just minutes on the EFI engines. With an old school carb and distributor it can take all day to dial in an engine. Even with a distributor machine it is painful to try different timing curves. Also, if you need stuff like start retard, high speed retard, two step, nitrous control, etc. you have to add a bunch of modules if you have a carb and distributor. If you have a good EFI system that stuff is all built in. The good EFI systems also have built in data logger so that is even more stuff that you don't need to buy and wire in.