He spelled "ridiculous" correctly. That surprises me.
The speeds are correct in AH. Altitude affects max speed due to drag and power delivered by the engine. Power delivered by the engine depends on the critical altitude(s) of the supercharger blower. In turbocharged aircraft such as the P-38 and B-17 you seen an even curve as the turbocharger provides a constant additional level of air preasure.
On the main page at:
http://www.hitechcreations.com/frindex.html select "Planes, Vehicles, Boats" from the "GAME INFO" dropdown. That has the performance charts for each aircraft.
When testing aircraft in game, give them plenty of time to accelerate to maximum speed as acceleration becomes very slow as induced drag nears the thrust the aircraft produces.