nah my flow NXT FSs are lighter then 390s lol...union contacts are wayyyy lighter then 390s, im not sure but i think nitro zeros are pretty light too. not saying 390s are a bad binding, or if its even possible to distinguish the weight difference between the 390s and contacts.
Union Contacts are the lightest I came across. But only get them if you have a soft jib board because the bottom cushion lets the board flex smoothly. I've picked up K2 auto's and Rome 390's and they're not even close.