Bf109E-3

[Winger]

Try lowering the pitch so RPM are around 2100-2300 and ATA around 1.3 Throttle to full. Youll constantly have to adjust the pitch in order to maintain RPM while velocity increases. It takes a bit but it should get you to 450 at least at sea level.
It feels a bit like accelerating in a car using a high gear. In fact its nothing else.
Just as a hint. I use a Thrustmaster hotas Warthog. It has a dual throttle lever. For 1 engine planes i set the left throttle to actually be throttle and the right one to prop pitch. In fact during combat i most of the time regulate RPM via pitch. Not throttle.

Winger