The factory manifolds (assuming iron) are made for low end grunt more than anything else.
I like the Air Gaps, you will lose about 20# of dead weight, probably lose a bit on the very bottom end, but jets dont use anything at the very bottom...

You should pick up a little in the Ass O Nometer in the upper RPMs.The one negative on the Air Gap type manifolds is condensation in the crankcase, as long as you have good oil temps, it's non issue.
Be careful to follow the factory recommended torque sequence when installing an aluminum manifold no matter what you decide...
X2 on the bigger carb if you go with an Air Gap, the whole idea is to get it to work less to get more air, not quite lipstick on a pig, but more like a pair of thong panties you can't see....

GT