Carb choice for high altitude?

Being a pilot A/F mixture is critical to maintain proper performance of a naturally aspirated engine. Mopekid is right about vacuum at higher altitude. Later larger carb won't give you more HP at higher altitude due to air density. Fuel injection is the way go go if you can afford it for operating at higher altitude. Lean out your AFB to achieve optimum H/p and go for it. Or you can always slap a turbo on it to increase the amount of air you can force into the cylinders as well as fuel.