Chilled fuel does two things
1) Increases fuel density - equal more power per given volume of fuel
2) Decreases flow time through the refueling rig - might save a 10th or two
I don't think that getting the air into the engine is as much a limiting factor as much as how quiickly the fuel can be injected. The window is incredibly short at 19,000 rpm to get the injector to complete it's duty cycle in time for the spark to light off and get the fuel burned (though the spark fires well before the duty cycle is complete - there's just not enough time). The FIA limits fuel rail pressures as a safety issue, so for a given number of milliseconds that the injector has to fire, a denser fuel charge will deliver a significantly greater amount of fuel than one at ambient temp.
Estimates I've read put this at about 10-15 HP for fuel that is 10 degree celiues less than the Sao Paulo ambient.
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