concerning flap load relief from 40 to 30: at least 30 is a "allowed" landing flap setting while if you are on 25 (due to load relief from 30) you basically are NOT in landing config.
on a gusty day where speed is hard to control there will also be little discussion about not having set Vref30 etc pp
but after some years flying the 738 to windy destinations i never had a case where 40 was set and landing was 30. also keep in mind the risk of flaps going back to 40 during speed decrease in flare.
when i started on the 73G/738 i preffered 30. didn't like difference in handling and visual segment. felt like to entirely different planes.
NOW i only do 40's. except that one runway where our company recommends 30 in the one landing direction due to tricky wind conditions during flare.
for me 40 is more practical on short or wet runways. also makes more sense. you don't want to be fast for landing, you want to be slow. landing means decreasing speed and altitude to zero, no need for those extra 7 knots.
by the way the idea of flying faster just to get less body attitude on landing is another example of poor engineering, nothing else. the 737 got a lot bigger since 1968, but rarely better.
and one more thing: drag with f40 is so high that it practically doesn't FLOAT when your app was on speed and you cut the power. especially with winglets and flaps30 that thing floats like hell.