BMW - 255-268hp @ 6600 rpm, 230 lb-ft @ 2600 rpm
GM - 270hp @ 6900 rpm, 223 lb-ft @ 5100 rpm (RWD applications)
Both VVT, DI. Both very smooth, freely revving engines. The BMW has a better sound. On paper it makes more torque at a lower rpm. I've only ever driven a much lighter, and less powerful, 328ix (and not a similar to the CTS but still lighter 528), I honestly cannot say whether or not that you could feel the difference. I would loved to have seen an ATS with the 3.0L V6/manual combo - but that will never be.