to be fair, the M1 and air gap are an apples and oranges comparison. They are both intake manifolds, but they are a completely different design, much like the kegger is a completely different design, that has it's special purpose.
the M1 is a single plane, the air gap a dual plane, and the kegger, well, is a lightweight boat anchor to most!(seriously, what kind of manifold is the kegger considered?an inverted-cross-tunnel-ram?)
A dual plane generally has a smaller plenum volume, due to having two separate plenums, and longer runners. This results in a manifold that's meant for lower RPM ranges, and is a good performer across most of the powerband. Sure, it's lackluster up top, but it's great for offroaders, daily commuters, and light to light racing.
a single plane generally will have shorter runners than a dual plane, and a larger plenum volume, that lends itself well to higher RPM usage. It will be a little weaker at lower RPMs than a dual plane(this is, of course, assuming the dual plane has signifigantly longer runners than the single plane) but wont run out of juice up top as fast as the dual plane would. Due to the larger plenum size, it will have slightly worse throttle response.
A tunnel ram has the shortest runners, and the largest plenum volume. they are generally quite large with multiple carbs/TBs, quite tall, and are for the most dedicated racers. They are the hardest to tune, due to the extreme plenum volume they typically have terrible throttle response, even more so when carb'ed. You can pretty much forget about a tunnel ram, unless you're Bad425RT and running an R3 block with W-series heads and a sheet metal intake. To my knowledge, no one makes an EFI tunnel ram for our trucks, and I wouldn't want one anyways. Tunnel rams are for extreme RPM situations, where you'd be running a 4000+ RPM stall, and spin to 10,000+ RPMs
there's a couple other common intake designs, but I wont go into them as they aren't very relevant.
Anyways, I know this is all very vague and all, I just had to point out that even if they make the same power, they are not the same animal
Also, since manifolds are 'tuned' for a certain RPM range, it's best to coordinate your manifold, headers, and cam so they all work together, so an intake swap, without changing the cam and headers, really wont do that much. Even on a bone stock truck, changing only the manifold is a very unfair comparison, except for the stock manifold, the parts in place are designed to work with it. That's why people have horrible results with the 4bbl M1 on otherwise stock trucks. It just simply isnt designed to work in conjunction with the installed parts.
