Pure guess: TCP/IP is a protocol that is a few layers above direct socket calls. So I would *EXPECT* that the direct socket calls would be a shade faster. Mind you the TCP/IP protocol has overhead on a packet basis, so if your transfers will fit within one or a few packets I wouldn't expect the overhead to be much noticeable.
But I haven't used Linux in about 10 years so I'm possibly way out of date and/or my memory is faulty.
An optimist sees the glass as half full.
A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.