4.8iS brake calipers and wheel sizes

[Clockwork]

TL,DR (Too Long, Didn't Read) summary:
Can a 4.8iS run 18" wheels or will the front Calipers interfere with wheel's Inside Diameter? I assume, the offset of said wheels would have to be lower (say 25mm and smaller even, to ensure the caliper doesnt strike backside of spoke)

I did find this thread https://xoutpost.com/bmw-sav-forums/...els-4-6is.html so there is hope that some 18's fit...

Hi all, I have a 2005 4.4i and ran 18" wheels with winter tires and OE 20" factory wheels with summer tires in.... you guessed it.

then I bought big beautiful 20" BBS CH-R wheels for a STEAL of a deal (and yes they are authentic, as I couldnt believe the sale, but older guy was just looking to offload them from his 7er. anyhow, now I have a 20" set of wheels for summer and winter...

SO I decided to upgrade my front calipers to the larger 4.8iS calipers. Awesome looking, bigger brakes and well not much difference for city driving, but oh well I did it anyhow.
SO now that I'm using this X5 for camping on dirt roads, the Summer tires on 20" wheels are making me worry a bit about the undue stress the steering and suspension components (damn near all new as I really take care of my X5). I want to buy a smaller set of wheels and fatter sidewall tires to give more sidewall comfort to the drive and allow the road bumps to get lost in the rubber instead of being transferred into the rubber bushings/balljoints/ride feel.
I am thinking a 19" wheel (I'm ONLY willing to buy BBS or OE BMW wheels) will be the smallest, but was hoping to get buy--in from OTHERS who have 19" OR perhaps 18" wheels on e53's with 4.8iS front calipers installed.
Thanks for your input, all.