The AMG 55 engine is a great power unit, I had the E55 AMG and loved the car, such fun to drive, mine had done a fair few miles and when it needed some work (O2 sensors) they were very expensive but if you are going to drive an AMG this is part of the deal but given the spend on your RR you know this lol
I have since owned S500, SL 500 and I have never been disappointed with the amount of car you get for the money, I actually think the big engine Mercs offer the best bang for buck in so many ways
There is a CL600 for sale at a dealer in Yardley, only 60K miles and all this car for £4K, very tempting