Thank you Avionero, that's helpful.
What concerns me about comparing METARs with crosswind limits is the tolerance on wind direction -- variations of +/- 30 degrees don't even get a mention in the METAR, but it can make a big difference to the crosswind component. Where there's a xxxVxxx group, do you take the worst case, or do you ignore the directional variation and just use the mean?
Example:
METAR GCLA 061600Z 23025G40KT 170V280 7000 -DZ FEW025 SCT045 BKN180 23/10 Q1003=
What's the relevant crosswind on runway 19 at La Palma (centreline about 180 true, I think)?