There were 2 types of engines used by LW - Db601A and DB601Aa which had little different power output.
Db 601A - sea level
1 minut emergency (2400 RPM at 1.4 Ata) - 1100 PS
5 minut emergency (2400 RPM at 1.3 Ata) - 990 PS
Db601Aa - sea level
1 minut emergency (2500 RPM at 1.45 Ata) - 1175 PS
5 minut emergency (2400 RPM at 1.35 Ata) - 1015 PS
Standart 109 E-3 with Db601 at 1.3 Ata 2400 RPM (5 minut power) reached at sea level - 467 km/h ( radiator 1/4 open)
http://kurfurst.org/Performance_test...MP16feb39.html
It is good agreement with Swiss 109 E-3 Db601Aa tested with different propellers:
Sea level speed - 467 km/h with standart propeller
Quite close with tested captured 109 E-3 by French :
So it could be that with Db601 Aa at 1.45 Ata 2500 RPM (radiator close?) - 1 minut emergency power 109 E-3 reached 500 km/h like in German manual:
Interesting is that at low level 109 E-3 need 5-minut power output with speed 467 km/h comparing to Spitfire MK1 at 6 1/2 lbs ( 1/2 hour limit) - 455 km/h. Db 601A had 990 HP at 1.3 Ata where Merlin III had 880 HP at 6 1/2 lbs at sea level.