..on WWII Aircraft Performance. In the most recent update, we finally have data about the Fw-190A-2 (BMW-801C engine) - 410 km/h even without polishing, then about the Fw-190 with external intakes and reduced armament etc. Plus plenty of A-4, (new) A-5 and A-8 test reports.
I remember seeing the Fw-190 with such cowling paintwork, but the hi-alt Fw-190As have had the external air intakes (picture), not internal as the ones from your article.
The service aircraft, featuring ext. intakes, retained full weaponry, so the speed gain at high altitudes was not as big as with the tested aircraft (with two cannons only).
AN interesting conclusion can be drawn from the report about the Fw-190A-2, ie. the one with BMW-801C engine. The table posted here states that maximum rpm in high gear was 2550, however that report states that engine was revved up to 2700 rpm at 5700 m and above (with ram). In other words, instead of 1380 PS at 4.6 km*, the power was pretty close to what the un-restricted BMW-801D was capable for (1440 PS at 5.7 km*) - maybe around 1420-1430 PS at 5.2 - 5.4 km*?
Seems that Fw-190A was every bit as good as it was claimed for it.