photos of the 38's would explain "knackered" better than words .
Usually folks will go the other way , from 34 to 38mm.
34's come with their own weird but are actually better documented .
You will loose a "bit" of top end that doesn't ordinarily get used anyway while moving the torque peak a little lower .
So , a good swap ? Apples to oranges , yes . Apples to apples not really but that is actually more of a subjective opinion . I'd use the 38's if at all possible but wouldn't call the 34's junk by any stretch .
~kop