Depends what you use the A4? If you drive loads stick with 45's if its pleasure cruisng and show time 40's.
Plus TBH pot holes are pissing me off these days

I'm not a fan of stretch, but as a show piece they look good!
You could still run 45's and tweak the suspension and arch more costly though!
Or lower directly onto 40's either way you will spend on 40's or new suspension set up rolled arches.
