I'm in the middle of upgrading the family cars and as the wife is after a CLK convertible, I'm going to have to get a family car capable of carrying 5 of us.

Having looked at what's on offer in my budget (£17.5k), I'm looking towards a C5 RS6 or W211 E55 AMG. Has anyone on here run either of these? What are the running costs like as I've heard some horror stories about the RS6's.