MiG-1/3: how good/bad it really was

The Bf 109E speed curves are a bit strange - 601A engine with initial 4km supercharger?

Probably so. The speed data I've plotted was dated as of 1939.
added: both French and Swiss tests give the 5 km as the altiude of max speed, and that is 550 km/h. Swiss tests were performed with Aa engine, that one was slightly better than the old DB-601A on all altitudes, and slightly worse than new 601A above 4,5 km.

In addition to the political side - which in Russia is and was a massive issue. As the war progressed the heights for combat generally overall, came down to lower levels. Priorities for development for combat will have changed given the fluidity of war.The influx of Foreign equipment had an impact with the Russians, especially the spitfire IX. Even though Russians were 'advised' to believe that foreign equipment was on balance 'inferior' to home grown products, as with most combatants there is generally a recognition of when somethings good its good. While the LAG's and Yak's were great down below, with the IX you got in a plane that was good pretty much at all heights and some good accounts of Russian Pilots show their appreciation of getting in a IX and just climbing and climbing in it appreciating that there was little in the way of drop off.

Privately, Soviet pilots appreciated most, if not all of Western hardware. Radios worked, the varinace in fit finnish was much smaller than in Soviet-made aircraft, performance was good. The tanks were mostly well regarded, too; Sherman was considered as a luxurious tank, for example. Valentine was also a prized item.

tomo pauk said:

Privately, Soviet pilots appreciated most, if not all of Western hardware. Radios worked, the varinace in fit finnish was much smaller than in Soviet-made aircraft, performance was good. The tanks were mostly well regarded, too; Sherman was considered as a luxurious tank, for example. Valentine was also a prized item.

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Absolutely - even designs we regarded as somewhat past it or obsolete, so to speak. The valentine is a great example.