Remember those meaningless "Slow down!" Messages you get anytime you're "faster than allowed" near gravity wells?
While you see your speed decrease due to the gravity well, you yelling "No, speed up!!" and having the Throttle slammed to maximum?
So how about this :
- you still can use SCA or use optimal Throttle
- BUT you could throttle up and not only exceed the rated speed but also the rated acceleration which continues to increase beyond the normal limits (distance to nearest gravity well or star)
...HOWEVER, at the price of increasingly losing directional control and the Ship veering to much off course (using it should start overheating the FSD and worst-case in a damaging dropout from SC when hard limits are exceeded).
Highspeed travel would be possible, but only with manual and increasingly skilled Control Inputs (keeping the Ship centered and on course), hot builds/Ships might have to limit the application as well in order not to overheat eventually.
So... how fast can you go if you're in a hurry? Depends. Skill and Risk Aversion.
Might end up evading that nasty Interdictor lining up behind you - but if you mess up, you might face leaving behind a Low Wake and 40sec of sweating while your FSD timer clocks down.
An Interdictor as well might make a dash for a juicy target.... but again comes at a price of having the overspeed controls interfering with the Interdiction Minigame and of course possible embarassment of dropping out of SC as well if things go downhill.
Should work in ways that doesn't make i.e. a clumsy T9 a disadvantaged ride (bigger rig, less swivel; heat might be a bigger issue eventually).
Basically very similar as how Ships already react to SC in a Neutron Cone - just with variable intensity, based on how far you push it.
On top, massively overspeeding near a gravity well could (optional) result in a very notable heat spike as well, as the FSD is now additionally pushed well beyond its normal envelope.
Something like that would work and give a few Options to be literally active on the Controls during longer SC travels.
Want to go faster? Sure. Want to go alot faster? Try it - IF you can control it....