I flew a Merlin IIIB with Dash 10s, 900SHP.
Cruise TAS running just under redline temp was always from 275-300KTAS from the FL160-FL250 depending on OAT and Pressure naturally.
The Dash 11 is 1000SHP?
Some TPE 331engine model comparison specs here-
https://www.e-engines.honeywell.com/...rod_specb.html
Sorry I cannot find the formula, I swore I had it here somewhere but basically, IIRC in a given airframe, both the same, the extra speed you gain varies with the cube of the avail power, all other factors being equal.
So if you wanted to double your original speed you need approx 8 TIMES the avail power!!
So if you had theoretically say 1800hp avail and now you have 2000hp, only an 11% increase so the additional TAS will be only a few kts above the prior speed.
An example would be in WW 2 , say in Spitfires, where the approx same config airframe, although heavier etc went from basically 1000BHP and a max speed of approx 350mph to over 2100 BHP in later models but max level speeds only went up approx 100mph for double the avail power.
As I said just a very,basic approximation and a simplified formula.It is out on the net somewhere, it is used in aircraft design. If anyone can find it I would appreciate the link.
