I read somewhere that the prototype XF6F-1 was marginally slower than the captured A6M2. For that reason the engine was changed from the R-2600 to the R-2800. Is this true? I find it hard to believe the performance between the R-2600 and the R-2800 powered F6F was that different. What was the performance of the XF6F-1? What was the reason for the change of engines if it wasn't to up the performance of the F6F?