After playing around with it for a bit, it feels like you simply have to multiply your hipfire sens by 10 to get the same vehicle sens. This also puts your ingame vehicle sens to the same as your ingame hipfire sens, further backing my theory.
On a different note, does USA feel weird for anyone else?
I played on 133% in BF4 and loved it, but now it feels too fast, I have a lot of trouble tracking people. Turning USA off feels better (The calculator tells me USA off decreases my sens for low magnification sights compared to USA on, so that makes sense), although not perfect.
It might be due to the lower FOV for the sights compared to BF4, but on the other hand, USA should make that a non-issue in theory.