as i said there is a simple way to go about this
a flat reduction to the thrust output of all thrusters by 25% or 50% should do the trick
No it wouldn't, it would wreak havoc on all game balance, and not just like my suggestion have a big impact on lategame balance for extremely fast objects ( only missiles or possibly some fighters )...
As you point out yourself further down the post listing a few of all the things that need to change like fuel efficiency. But we also have fire controls ability to hit ships, fighters and missiles lower techs, distances and travel time, ability to escape black holes pull, how harsh nebula's impact ship speeds, trade income from shipping and the list never ends.
At least consider fixing only what you think is broken ( extreme missiles ), and not breaking all balance in the entire game at once?
And Paul M, isn't 2% noticeable for 0.2C ?
As you say the big impact only happens at 0.75C which is precisely when amimai is starting to notice problems ( and as a solution wants to cut all thrust by factor 0.25 ).