[pavulon]

To me (not an authority), taking on an Audi project would be a much larger commitment ($$$$) unless you were to simply turn up the wick a bit on the original drive train configuration. The quattro system pushes the engine way out front too. I love the sound of an angry turbo 5 with anti-lag though!

A rwd BMW seems to offer a lot more flexibility. As you likely know, the "LS swap all the things" crowd has made that route much more straight forward which would be a lot less $$, frustration and opportunity for project loss of interest or abandonment. Even if you wanted to be a purist, a euro s50 E36 M3 sedan could be pretty amazing and are approaching 25 years old for straight up importation to the US.