Yeah, you're right about that. I'll be running a track optimized square setup. Which means I'll be going for a slight stretch on my tires. As long as my wheels clear the struts I should be good.Probably not much or any more than 12mm. Which why the PP rears don't fit up front.
Front strut clearance is the biggest limiting factor to fitting large tires on a s550. The last thing you want is wheels that make it worse.