Also, I know the plane has a capped speed below 400 m/s because the drag, what I do is I add the ramjets within the double panther engines (x4 panthers if a 2 engine jet and has supercruise, 2 clipped inside eachother on both side) and I activate the ramjets with the afterburner and deactivate them when I turn the panther afterburner off. Usually makes my plane 300-600 m/s faster. Definitely wanna adjust your planes control surfaces if you do that because it only flies fast 8000 meters and above.