A few thoughts from my experiments with carbs over the last few years, FWIW (on a 56 sunliner with 292/F/M)
The holley 390 is easy to tune, but hruns out of breath at higher RPMs. Mathematically it probably shouldnt, but in back to back runs vs an edelbrock 500 cfm, ithad noticeably less top end power. However, id had better throttle response and started easier.
Edelbrock 500 carb - pretty easy to tune once you figure it out, good top end power, not very crisp throttle response, and a really slight stumble if you try to cruise slowly right after idle/tip in. Its been that way on every carter/edelbrock ive ever worked on or ridden in....not noticeable unless you do a lot of slow speed cruising (i.e. parades, etc, and even then its not bad/embarassing/bothersome..its just there)
Demon - I tried the route of getting a reman demon from Jegs. It was a mess. Missing retainer clip on the secondary rod, beat up float bowls, god knows what else. To their credit, Jegs immediately offered to sell me a new one at the same price, and I returned the reman. However, the new one has been crap too. Ive not been able to get it to run right, and every time I take it apart to change jets, PV, etc, I find more and more metal filings/shavings and gasked chaff floating around in there. As soon as I get the car running again, IM going to give it one more try and if i cant get it to work, im going to call jegs again to see if they will swap it or what... really disappointing, as most people rave about demons.
Just a few thoughts, FWIW
Ron Grove
Wauconda, IL