"Optimum Accuracy" is achieved through a balance between velocity and spin rate.
So you need enough spin to stabilize the bullet at the intended velocity.
If your spin rate is too slow for the bullet, then you would not be able to achieve the speed required to achieve gyroscopic stability, and accuracy would suck.
If your spin rate is too fast, the accuracy tends to suffer as the bullet goes into a speed wobble of sorts.
In the case of a spin rate being too fast, you can always go with a faster burning powder an run at a lower velocity, then you could still get good accuracy with light bullets from a fast twist. Just reduce the velocity until they are accurate... and don't fly apart 1/2 way to the target.
I'm not sure why you might want to run light bullets from a fast twist in the first place as it's realy just an effort to castrate what might otherwise be a long range rifle.... but hey... to each his own I suppose.
People neuter their cats and dogs too.
Nobody ever uses light bullets for long range competition and there's a reason for that, but you can use heavy bullets up close.
Flat trajectory at close range is over rated.
Reducing the effects of wind deflection at long range tends to be under rated.
So even if you get decent accuracy at 100 yards, don't expect light bullets to shoot worth a darn at 300 yards or more.