Yes, the R8 and Bentley both suck. Honestly, what's the point of stuff like this. At this overall level of car, it is all subjective. All these cars are superb and will all have their strengths and weaknesses.
I guarantee that if you take 100 drivers who have driven neither car ever before, and make them do a track session, the vast majority will turn faster lap times in the R8. Maybe a hand full of super-skilled people will be able to get the M3 around faster.
Most people who buy a Bentley are also seeking a level of luxury and exclusivity way beyond the M3.
If you want to drag, just get a GTR, Viper, Vette, Shelby, etc. and call it a day.
Audi S6 * Audi S3 * Porsche Cayman GTS
--Former BMW M3 owner