Put 100k miles on the M and 80k on the RS
Brake costs are similar
On the RS the front pad retaining pins hit the rotor before the wear sensor so keep on eye on it. With oem pads the rotors should last 100k. I changed mine at 60 iifc but the old were only 50% worn (a lot of highway miles)
drc mine was ok at 60k when I had Audi's free recall done
I had H&R springs installed at the time
mpg is similar
Oil changes similar
Tire costs similar
The M needs 30k valve adjustments, the RS has hyd lifters, I dyi'ed mine
The RS is deceptively fast, not sure about 'Ring times but my guess similar.
I have owned many BMW's and imho Audi quality, fit & finish is better
Should not have sold my RS (did not want the hassle of 2 cars) it was one of, if not the best, cars I've owned (w205 c63s, w204 c63, e39 m5, e36 m3, e30 m3, etc)
Thinking about getting another to replace my wife's mini clubman.
We'll share it (but that means she'll drive the c63s

Looking at this one https://www.autotrader.com/cars-for-sal ... pe=listing
Look at the carfax, 36 service records, dealer maintained