BMW says its new 645Ci is moving into an "unfulfilled niche", offering the performance of sports cars costing much more while at least matching other similarly salubrious luxury entries. The fact is, the latest BMW does not really have a low-$200K rival. But it does have serious dynamic as well as awesome touring abilities. Buyers of models as disparate as the Porsche 911 Carrera, Jaguar XJR sedan and Mercedes CL500 would be foolhardy to ignore it.