MW to 9 first

The magic damage formula works so that the more magic you have and the stronger spells you have, the more additional magic will affect your damage. Also, it only raises base stats, so take that into consideration if you're not lukless. Early MW would be most beneficial to luklesses with insane equipment. If you're low/normal luk and you don't have above average magic attack, then I'd suggest other skills before going for MW, since it won't really be as beneficial.

Just plug your magic attack and int with a certain spell into the formula, then plug in with your new magic attack and int after a theoretical level 9 MW (5%) and see the difference. The difference will be shown the most from blizzard.