Hmmmm. I'm doing a bit of research and something seems off: the Bf-109D (the relatively few built with 960 hp DB-600As) had a top speed of 323 mp/h (520 km/h). This aircraft is getting almost the same speed out of 2/3rd the horsepower, from a less-streamlined radial engine (though it is lighter). Is this a case of Planebuilder being better than reality?