is it possible to have the air too warm for fuel economy? has anybody experimented with temperatures to find an optimal temperature?
Sure. If your intake air is too warm, you will start to get detonation, just as if your car is overheating. How warm is too warm? Depends on the vehicle. I have never experimented with different systems on the same vehicle. My short ram intake on my 2008 Civic Si served as a warm air intake. I saw intake temps soaring to 144 degrees F during 100+ degree weather last summer. That was as high as I got, and the car ran just fine. Power was slightly limited, but mpg was nearly 40 (car was rated at 29 highway).
Note: That Civic was a modern car with a premium fuel appetite (which helps mitigate detonation). The fact that it was a newer car means that it has knock sensors to help change ignition timing to keep detonation from occurring.