Very nice, yes...
From "Samoliotostroïeniyé", the TsAGI book, Jookovski editions. That's the limit (for T and others) to send datas even without knowing where there a taken from. In that case, a copiright (c) should be mentionned...
Yes, they are. Soviets used a full half squadron of captured Doras.
It's seems so. Other indicators from the book, page 95:
631 km/h at 6150 m
(642 km/h at 6100 m) "forced" rating
Mentions of power at rated alt:
1480 hp
(1600 hp combat rating)
.