For the sake of a discussion let us look at a few numbers and see what they mean. The big iron (15cc) should weigh about 5 lbs. and carry at least a 1/2 lb. of fuel. From previous posts terminal velocity of the dives were hitting 290 mph. This means that gravity was contributing about 4.2 hp. Two stroke racing engines have an output power of about 7 hp./C.I., so a .91 should produce about 6.4 hp. However, about the best you can hope for in a prop is a conversion efficiency of about 85%, so the engine/prop is really doing roughly 5.4 hp. When you add up the power from the engine/prop and the dive you end up with 9.6 hp. achieving the 290 mph terminal velocity. So with only 56% of the power available when flown level, the airplane should be capable of about 235-240 mph. Any speed above this is due to energy carried over from the dive.
Caveats: More weight, slower level flight speed. Lower efficiency prop than 85%, also slower level flight speed. Less than 6.4 hp. from engine, well you get the idea.
One final thought, if you pull out of the dive about 1/2 second before a vertical planting, that would imply about a 250 ft. radius. At that speed (290 mph), the model would be pulling in excess of 20 g's (at least initially). In the earlier Speedcups, I noticed that the .40 sized FAI pylon ships were nearly as fast as the heavy iron. It would appear that a higher aspect wing would help maintain energy from the dive.