Sorry but these 'mechanics' have it all and entirely WRONG !!!!!

Too small a filter means NOT too small a retention rating but too small
a SURFACE AREA of the filter. What kills the lift (or any other) pump is
particulate and continually working against a high differential pressure
caused by either too small or too plugged a filter.

If you have a dirty tank or a tank without a recirculation filter use:
30uM followed by 10uM followed by 2uM ... the 2uM can be the 'guard'
filter between lift and high pressure pumps.

If you double the surface area, the differential pressure needed to
operate the filter at the design flow will be HALF .... and the service
life (to plugging) will be approximately *FOUR* times longer; plus, the
particles will be stopped on the filter media! The higher the
differential pressure the greater the possibility to extrude soft and
deformable particulate through the filter media.... only to plug a finer
rated filter / orfice, etc. downstream.

Of course you MUST in all cases monitor the performance of such filters
with pressure/vacuum gauges ... and check them periodically to develop a
plot of lifetime vs. time/gallons in service and WHEN to change them.
Bigger filters will SAVE you $$$$ and 'sudden' headaches, are more cost
effective and "removal efficient" than changing out teeny (and just as
expensive) filters on a 'seasonal' basis. Change when the pressure
gauges tell you to change them, install at least the next LARGER
*surface area* filter recommended, ............ instead of waiting for
the filters to plug ... when the weather is very rough/severe, you NEED
the engine to keep moving for safety, you and your crew are
seasick/tired/terrorized/etc.... and on top of this you have to go below
and change the filters then bleed the system - all the while you're
projectile-puking great lumps into the smelly bilge. That's not my idea
of fun!

Better yet is to install a recirculation filter with an integral gravity
water knock-out pot ... then you only need a regularly sized final
filter, will have no bacteria/water/particulate/sudden power
loss/etc./etc./etc.
You can wire such a system so that the recirc. pump operates any time
the engine is operating.

Hope this helps.