A/G?
What kind of A/G: interdiction, CAS or carpet bombing of cities?
In a TIC (troops in contact) CAS scenario as long as the asset is over head they could care less if it was supersonic (SS) or not.
Recent wars have shaped our view of air assets. US troops have not been attacked from the air in decades. In all recent US wars the US has had total air superiority. An A10 is an awesome CAS asset, and the ground folks love it. If you don' have air superiority a SS multi-role asset (F16, F18 etc) may be a better choice.
Speed improves the effectiveness of stealth, as long as IR signature doesn't compromise it.
Aircraft design is one big compromise. In the tactical arena if the aircraft can't survive it doesn't matter how good an AG asset it is.
Guess I am leaning towards a SS capable aircraft.
Cheers,
Gerz