I am probably the worst person for going over the top and I know Keith Craft has built me a very good SBF engine that produces well over 600bhp on pump gas, we have had the engine running on the dyno here and its everything I asked for and more! This 358 based engine has 320bhp @ 4000rpm and then it increases by a whopping 200bhp by 5000rpm to 520bhp and then all the way to 600+bhp, and very smooth.
I know its going to be a bit like Jay Leno's 427 Cobra on the street very lumpy and then WOOOOOOOOOOOOW.
I ran a genuine 270 -300bhp in a 289 Mustang engined Zephyr car many years ago and what a delightful free revving kick in the pants engine, so to my mind it all depends on the combination of gearing, transmission etc, I would go for the original Cobra horsepower with more reliability, as for eg a friend has a FE390 Cobra which would be very lucky to have 350 hp and quite frankly its not enough, but if that was a SBF it would be plenty and very lively in a Cobra.
FE390 -427 for the street strive for 450bhp!!
Driveability if you can hop in the car without thinking and go on a run thats what you want, but in my case it will be limited road use and when I do care and attention to preheat the
oil and warm up nice etc etc, but I intend on doing some runs like a similar car on CC, John Marsey he has a similar setup in the JBL Boss and he enjoys giving it a blast.