Unless I've lost my mind, I've heard that stock offset is 43 mm. If that's the case, then the difference isn't as much as you're thinking now -- which isn't much of a difference anyway, so you can rest easy with either number.
People don't seem to be having problems with 225's, with or without a drop. Either of the sizes you mention would work, too. The wider one would obviously give more grip, but it'll follow road irregularities a tad more. I'm getting 205/50's on 16x7 rims in a few days myself.
Reviews on Tire Rack favor the Kumho 712's over the Yokohama AVS ES100, so I would go with those. However, they seem to like Ecsta 711's even better, which is what I'm getting after all. 711's aren't made in V or Z speed ratings anymore (they're H-rated now), but usually that just won't matter.
Falken seems to make good stuff, too.
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