As with anything, it depends on a lot of factors. Which carb(s) you're running and how they're tuned, which EFI you're running and how it's tuned, some of the ancillary hardware. Back in the day I was into 80s V12 Jaguars, which kept the ECU in the trunk, a good 10-15 feet from the engine. The MAP sensor was located on the ECU, with a vacuum line that ran all the way up to the intake manifold. So the real lag you had was the physical lag of the pressure in that vacuum line changing over the course of those 15 feet, which made the engine noticeably less responsive for rapid power changes. Although I did make it shoot fire out of the exhaust pipes a few times when doing rapid shifts from high RPMs. In this case, I'm looking at running velocity stack EFI where it looks like Webers (would be my preference but they're too pricey) but is actually EFI. One factor in responsiveness is the distance between the throttle body and the intake valve, and so velocity stacks with independent throttle bodies only a few inches from the intake valve will help responsiveness. Since I'll be programming the EFI I'll also be more generous with the throttle tip-in enrichment which will help. If I wasn't going to do the velocity stacks, I'd just pick a conventional intake and probably an Edelbrock carb. I think the end result is going to be pretty snappy all around. I was thinking about the closest vehicle to the Cobra that I've driven in the past, and it was the '93 RX-7 twin-turbo. The one I drove was a low mile, completely stock car - beautiful. Now, the rating on that car was about 255 HP (compared to the 400ish I'm looking at), and looking at gearing I'll be a bit taller with 3.73s vs. 3.90s in the back, and then a bit taller gears in the transmission. Tire diameter I'll also be a bit bigger on. The 3rd gen RX-7 is fairly close in weight and overall size to the Cobra, and I thought that 400 HP would've been a good number for that car. So, I think I'll probably find that to be the case in the Cobra, too. I'm more and more thinking the 347 is going to be the way to go engine wise.