The BMW 6-series is a big, powerful car with very good handling, something BMW is known for. In convertible form, it makes for a fast open-air experience. For the 2010 year, the 650i picks up new BMW cabin tech, but still has last year's engine.
The 2010 650i is powered by the same 4.8-liter V-8 as the 2009 model. But the 650i lags behind BMW's 7-series in this regard, as the 750i uses a 4.4-liter V-8 with twin turbos, making substantially more power without sacrificing fuel economy.