It is purely subjective.If you've never tried either the current production or a NOS 5751,it may be worthwhile to try a current production first before you spend the $$ for a nos.To me the current production are dull and lifeless by comparison,like a weak chinese AX7.Even a used old stock 5751 is better.I have a good supply of various brand old stock 5751's and although some are better than others,in certain circuits the lesser ones are better than the "better" ones.If that makes sense.I have too many amps,so I can only be kind of general in my descriptions.Mavguy or Wolf can give you a clearer description of comparisons,they've done more extensive comparisons and are more discerning in their conclusions.You can do a search or,perhaps,they will chime in.