No turbo plans then the 17'+ have all the important upgrades to the chassis. A 14'-15' if you think you might turbo it, 16'+ might have weak rods that need to be changed before boosting. There were slight upgrades every year from 14-16' on the secondary clutch to chaincase shaft and bearings. 14' need the reverse detent update, but most should have had that done under warrenty, also the fuel filter clamps check.
ANY used viper should have the clutch side drive bearings checked/cleaned/greased before riding, and make sure it has the most up to date computer flash.