This Mercedes may just be the fastest open-top/convertible production car on the road.  With a top speed of 220.6mph, the McLaren 722S is the fastest Mercedes SLR yet. The 722S is powered by 650-hp supercharged 5.5L V8 engine that will force this Mercedes to unreal speeds on the high end.  Only 150 of the 722 S models will be sold, a number so limited that we’re a bit scared to see the price tag.  You’ve got a bit of time to save your pennies, though– the 722S won’t hit pavement until January 1. [mercedes via autoblog]