In some ways it seems the US Army ended up hedging it's bets well. For high altitude, they ended up with the P-38 P-47 (two different engines, another good hedge.) For low altitude they ended up with the P-39 P-40. On the other hand, they seemed to put all their eggs in one basket with turbochargers, almost an obsession. Perhaps it would have been better to hedge their bets and support a 2nd parallel program such as 2-stage supercharging? I suppose it could be argued that this would drain resources from turbocharger projects, but then one could argue that the P-47 drained resources from the P-38 project, etc.