the 460s will demonstrate a much lower noise floor than the 391b's, and have better quality mic amps. i do like both mics though, and have gotten excellent results from both sets. the 460s are particularly wonderful if modded by jim williams, and reach a quality simijlar to the 480s. however, the mods are not cheap, and i wouldnt hesitate to go with the 391s, depending on how good a deal you can find on a pair. i have done some very nice studio recordings with the blue line mics, and they are a favorite of some of the jazz musicians i work with.