The emergency and water injection power is a take-off power setting. It was available in real life in that role too, not as a continuous operating power setting.
Il-2 runways are too short to get substantial load off the ground otherwise. It's a bit of a tradeoff for gameplay.
The jet engines are set to have overdrive intentionally (I saw you took that out) to enable the player to push all engines into overdrive on take off with one control lever. With your FM, you can't go beyond 100% unless you control jets and props separately.
The current FM was judged with 100% power basically.
There I get top speeds of ~ 585 kph for B model and 725 kph for a H-III at 10K
Of course, if you burn continuously at 110%, you will go beyond, (and get ringing ears from the screaming wind noise) but that is not how you fly usually and not how you determine the "top speed".
If you look how the USAF rated their planes at the time it gets even more complex. The numbers are more complex than just a single top speed figure. The system took into account the weight of the aircraft (which is scaled down in Il-2 for the sake of being able to take off with any load at all), as the performance over target was deemed the essential. And these tables can't be reproduced 1:1 with what we have here. To interpret them is a science on its own, and definitely more complex than letting it run at 110% power for ten or more minutes. Measured by that rate you'd end up with a probably too weak aircraft in "normal" or "usual" operating settings.
As a pilot states, The peacemaker always had plenty of power if you needed any, it had an overpowered feel.
My 2 cents on why we left it that way.
But this is just fine, no argument against your FM, just some things we thought over when making it the first time.