Hi,
It simply was to smal to fit a more heavy engine(it already was heavy wingloaded with only 2500kg weight) and the so often shown Vmax was made with a unknown power, this datas often get compared with the combat/climb 109E4 speed.
Afaik there are no datas available under normal test conditions.
The He100, same like the Me209(109R) got used much for propaganda purpose, if this plane would have had such speeds without other bad disadvantages, latest in 1941 they would have looked for it. Even in 1943 its best datas are very good.
But i guess the datas are made with the 1700-1800hp engine, same like the Me109 in 1937, which reached 611km/h(not the 209)!
The normal He100D had a Db601M engine, which probably was similar to the DB601N or E and did need C3 fuel. So if someone wanna compare the He100, he need to use the E4N/E7N or F1 WEP datas!
This are the datas i found for the He100 D1:
2500kg max
14,4mē
DB601M 1175HP (dont know the altitude)
560km/h sea level
668km/h 6400m
1 x 20mm MGFFm
2 x 7,92mm MG17
I dont found any sources regarding plating, selfseling tanks etc.
At least the ground crew disliked the airframe, cause it was difficult to maintance and the pilots was suprised about the very fast landing speed and long time to stop(actually i dont consider that as a problem, later planes was even more heavy and did need more space).
At a time when the LW still did need propaganda, the 109 also was claimed to be much faster(several world records etc), but as we know a real combat worthy plane perform much more bad than the unarmed prototype!
Greetings,