"SP-CMC-8 cards > SP BB > mic in > PMD-620. Limiter on -24db, recording levels peaking around -12 db, low cut filter off."
Looks to me like your battery box is providing power to the mics, so there is no real reason to use mic in unless your levels aren't getting you enough volume. I would recommend setting up 3 presets for line in: one at 0db, one at -12db & one at -24 db.
run the same setup line in in a club with a band where you don't care about the results. Start on the first preset and see where your levels go. If at 0db of attenuation you can't get enough volume, go to the next preset (-12db) and try that.
the pmd 620 looks at every thing as CUTTING decibels. so line in at the 0db pad with the volume all the way up is volume at 0.
when you turn it down it's -1db, -2db all the way to 24.
what i like to do is find the volume & pad setting that lets me run line in with the actual adjustable-by-increment volume set about -10.
that way when it gets louder I don't have to change to a different preset, but simply switch off the hold switch and adjust accordingly and there are several dibs to go in either direction.
in my experience, that's the best way to use that setup.
mic in will be slightly noisier, but not THAT much noisier.
i forget what the noise floor difference is, but its on a bunch of reviews from when the recorder came out.
after you've done that experiment (for the cost of bar admission & beers), go inspect the results and see if you like what you hear. It should be an accurate representation of what the mics sound like. They aren't crappy mics, and about 30 feet from a small PA should sound OK.
I think that's all exactly what everybody here just said, though.