I don't think i'll. I don't like FF cars . Some few are ok , but increasing power on those cars just turn them worst. Wheel spin....
For the same ride height :
Down = +more grip -power due to more PP
UP = - Less grip + power due to less PP
It's a compromise , Lap time on a given track will speak and will oriented you showing the best way.
Talking about stability , it's different problem.
For suden lost of grip due traction for example (losing rear end under acceleration out a corner) when you raise the car up, it tend to diminish this behavior , turning the car more stable.
Also you have to considere the ground effect of the car.
Road cars with no ground effect , flat bottom ... rear diffuser ... Low the car don't increase so much grip.
On a race car , yes .
Also you have to consider the rack of a car.
To resolve the same problem , increase grip , you have 2 options for the same PP.
-1st option :increasing front downforce for a given ride height
-2d option : Or setting a lower front ride height and lower front downforce.
The second option give the same grip than 1st option but increase stability.
Of course there is some special cases. Like
Ferrari 458 Italia GR3 '13 - Maxed PP - Racing Hard tires - Watkins Glenn 800 Event This car was very very unstable. For a normal stable car , i would set higher rear end. This car is very low on the suspension both end / and mini front downforce maxi rear downforce.
I hope i was more or less clear. It's difficult for me to put this on words.