Look at its main competitors, pretty much all the M powered BMW's are bi-turbos with massive power and the new M3 has been pretty much confirmed as been turbod aswell and all are suppost be more efficient than their last respective engines.
They should have put that 4.0 bi turbo V8 engine in from the Bentley Continental, basically a V8 block with 2x fsi heads and we all know the capabilities of the 2.0tsfi, imagine 2 side by side in an RS4