i cross referenced a few things, everything said 120/60 is stock.
if you got a 65 on there now, i doubt u would be able to tell the dif if you went to a 60 or a 70 since u said u arent a aggressive rider.
the rear is a 160/60 stock
160 is the width, 60 the aspect ratio/height, 17 is the rim size
so for the front, if you got a 65 now, then no matter what direction you go (120/60 or 120/70) its only a 5% change. width is the same, so no prob fitting the rim.
if u went with a 170/70 rear(itll fit the rim, but check the chain clearance and swingarm clearance) and a 120/60 front, u would be lowering the front a tiny bit, and raising the rear alil, so i would think if you did ride it hard enough to notice, it would steer a lil quicker. i never rode a sv, so i dont know if you would even notice it.
and heres the manual
www.carlsalter.com