Here's another good one too...this one gives you the opportunity to specify fender, wheelwell, and suspension clearances plus scrub radius...
https://www.wheel-size.com/calc/
Type: Posts; User: Muggy
Here's another good one too...this one gives you the opportunity to specify fender, wheelwell, and suspension clearances plus scrub radius...
https://www.wheel-size.com/calc/
Looks like OEM RS6 floating seat lug bolt is 28-30mm from tip of threads to base of ball..
http://www.fototime.com/C29DB9231188510/medium800.jpg
Pretty much all VW & Audi spec OEM that I know of are ball seat....aftermarkets are going to generally be cone/taper seats. So yes, you'll need to go back to ball seat if you go with OEM spec wheels.
You'll have a few fit issues with either of your posted options to consider...
First is an adapter for the center bore, not an issue as you can get them, but an added expense to a wheel setup....