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Foto dude, you really have to experiment, a close look in the VF and instant review are your best friends (almost typed 'fiends', might be a better description).
Anyway, for variable blue skies the Pol will accentuate the effect, it can be artistic, sometimes very off-putting. More often the best use is to quell reflections and glare, if you have the 2 stops to spare. 35mm looks pretty normal as a starting point, but it is all case specific sadly. No golden rules..