The RS5 will have a V8 but with new technology incoporated into it to improve performance and efficiency. In essence the RS5 is a coupe of the upcoming new A4 which will be larger than presnet A4. As the present RS4 has a V8 we can assume that the new RS4 with new MLP chassis will also have a V8. Makes no sence to give the RS5 a V10 as not a competitor to M6