I think since the Euromeister 17's are so new--no one has even seen them, much less put tires on them--that all the sage wisdom givers on this board are withholding judgement on them. That being said, if you want to keep the rolling diameter the same with the 17's as you have with your current wheels (and you probably do) than the largest tire to install will come down to what fits within that parameter. You'll definitely need a shorter sidewall. I am going with a 225/40 on 7x17's, to match the current 225/45 16's I have. It's not a perfect swap, but it's close enough. 225/40 17 tires are few and far between though.
I am interested to see how the Porsche community handles these wheels, considering the $$$$$ everyone has, here to now, spent on making 17" Fuchs. And how it's going to effect the "Big Name" Fuchs builders we all know and love here.