I was just looking at the Momentum GT vs the Magnum Stage 2 --- Interesting that the momentum seems to draw air from the outside, as a sealed unit .. yet the Magnum is more free flowing under the hood --- ehh.. I'm not sure which would be better.
Based off other CAIs I've installed it looks like the Magnum will reuse the OE air box - filter sits inside the box reusing the OE air scoop extending towards the grille while the polished aluminum heat shield top will snap onto the air box, like the OE top does. The Momentum GT will completely replace the OE setup and should be a fully sealed unit. From a heat rejection standpoint, both models are probably very comparable. What's interesting is aFe advertises the CFM of the Magnum but not the CFM of the Momentum GT.
If I were considering either aFe intakes, I'd ask them what each part numbers' filtration efficiency is. Then compare that filtration efficiency to our OE paper filters. Most aftermarket CAI will outflow the OE setup. The question is which option can outflow OE while also providing a higher rate of filtration efficiency. Sure there's a point of diminishing returns where the engine no longer benefits from the increased air flow, but as long as the filter is stopping dirt and dust more efficiently than OE, and it's something someone wants to install, they should do it. If you're going balls-out with upgraded turbos, a turboback exhaust setup, a tune and whatever else you're bolting onto that truck, there's probably a good chance your engine's combustion process will benefit from increased CFM over the OE intake.