Those charts hardly show the P-51 with 150 octane fuel being faster than a 109K-4. Rather, they give the appearance of their maximum speeds being about equal. The later 109K-4 props yielded speeds in excess of 450mph.
You have a point though. Our P-51D seems to be an early model without 150 octane fuel, in other words the worst representative of the series. There are a lot of aircraft in AH that are victims in a similar way: off the top of my head, the Spitfire Mk V and 109G-6.
Look at the charts again. At low altitude, where we fight in the game, the Mustang is significantly faster. Look at the the climb rates as well.
Not only do we have the lowest horsepower P-51D, we have the fastest 109K-4 (452 mph) version. I'd like to see the 150 octane fuel available for a moderate perk price (just like certain bombs and weapons should be perked), but only for those fighters that served in the ETO (P-47D-25, P-47D-40, P-38J, P-38L, P-51B and P-51D. Likewise for the late mark Spitfires. Adjust the perk value based upon ENY.
I know that the flap issues will be addressed eventually. Those issues being some aircraft with horrendous flaps and others with magical uber flaps. Once that is aligned, I believe we will see performance more in line with war time reality. That won't end the whining, but it will make it a lot tougher to make a valid case.
I'm not sure I would want to see G-suits modeled. Given a 1g to 2g blackout threshold advantage, I think it may unbalance the game. It did contribute to the imbalance in the war, no doubt. Should a 109 pull 5.5g at the ragged edge of blackout, but the P-51 behind can pull 7g, it'll greatly effect the result.
My regards,
Widewing