Depends. Is it your daily driver? If there is too much bhp and you want to really push it to the max you will be sacrificing the reliability of the car in comparison with a more modest modification. There are people on MBWorld who daily drive their E55. Some are running Euro charged HE, 180mm ASP Pulley, Some the Brabus K8 and others with just a more simple upgrades as filters and exhaust.

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2015 ML350 4Matic. Wifes DD
2015 GLK350 4Matic. My winter DD
2012 E350 4Matic. Road Trip car
2009 CLK350 Coupe Designo.Kleemann Tune For nice days/DD
2006 CL600. V12.Eurocharged Tune. Enough said
2005 CLK55 AMG Coupe.Kleemann Tune. For the sound and style
2004 CLK320 Cabriolet. 2005+ Interior swap. For the sunny Florida days & beach days