The SV is pretty stable no matter what, so unless you get totally out of hand with dropping the forks it won't jump around at high speeds (assuming you haven't raised the rear to an unacceptable level). You can experiment with it to see what you like. Just drop the forks 5mm and go ride it. If you like the change and it's still stable at high speed, then drop it another 5mm and try again. You might like that better, or might not. If so, leave it, if not, raise it back up 5mm and call it good. Watch the clearance with the front fender under hard braking and make sure you don't drop them so much that the fender hits the radiator.