It is actually pretty fast. I think they claim about 450 knots or so. Maybe not exactly correct but I remember being somewhat impressed at the claimed speed. Now, whether that is dirty or not I can’t say.
Maintenance costs would be interesting to compare as would average ready time...or whatever the Air Force call it.
450 knots is a target.
A better choice would be to update the A-10, if you want a subsonic ground attack aircraft.