I've thought a lot about this as well and have some 17x9 +35 wheels already (+30 would have been safer I think but can run spacers).
Im not at all concerned with outer clearance at the fenders, as Ive already rolled and pulled mine. Totally okay with flares and have a set of M2s in my garage.
Height clearance and suspension clearance is what frightens me. Have a hunch Woods247's 235 wide tire on 17x8 +30 and -3,0 camber up front solution might be the best bet.
Height is a hard one. My guess is that 245/40/17 might be pushing it already and the max you can go. Also which model tire you use can determine clearance. Hankook RS4's don't run so tall and are around 24.5ish in 245/40/17 vs closer to 24.8 for most other 200tw tires in including the 660s, Z3, a052s, etc. Go 255/40 and you're hitting maybe 25 and over. However RS4's also run wider too, which is not a good thing for suspension clearance.
On my end already have Meister coilovers with the tallest Swift spring combo but could only get as high as OEM maybe give or take a quarter inch. Could be wrong but doubt I will clear 25"
Suspension clearance is the scariest. Recall in another recent thread Woods mentioned there was 1/4" clearance to suspension with 3.0ish front camber w/ 235s. 245s and 17x9s would be even tighter.
Maybe 2.0 front camber would work, but then than is really not ideal for grip and tire wear for track and autoX use. You could get more aggressive offset, but that would not be great for turn in scrub radius.
I predict to make 17x9 work, would need offset closer to 25 and go with very short tires like the RS4s. Toyo makes a 200tw tire in 245/35. Flares would be needed more likely than not.
I think 16x8 with 225/45 and close to stock right height is best if you want to keep it simple without much work. Have 16x8 +38, 225/45/16 Z3's (23.8" height iirc). When at 2.0 camber had zero rubbing. Now at 2.9 and very slight rubbing up front that occurs only occasionally at full turn in. I have a hunch I'm hitting the bolt right at the fenders or the suspension.
215/17s on 17x9, no thank you. So depressing. But if you are doing this for car shows and to look cool only makes sense and that is a proven combo fitment wise.