At stock speeds, there's not much performance difference, but the Winchesters overclock better than Newcastles on S939, and the Newcastles do that better than the Clawhammers on S754. (The S754 3200+ and 3400+ Newcastle variants also have 200MHz on their Clawhammer counterparts, but half the cache.) Winnies also run slightly cooler than NCs on 939 and perform slightly better at the same clockspeed, but this is likely to be insignificant.