Worked out what was wrong....a less than sign was corrupting my post.
here goes...

Note: A 2004 E55 is stated at 470bhp (350kW) and 700Nm (520)
This is less than 10 percent more than what an equivalent amount of money and effort could achieve with the 3.2L running in the low 20's for psi. You add a few lbs in weight as well.
I believe the other V8 installs have been Normally aspirated ones- not Supercharged ones.
The 8 pots add more weight to the front end which leads to more understeer and less traction at the rear, but others may comment more.

PS - I know you have the engine/tranny at your disposal - but just to keep you thinking, have a look on google for RobertAMG's Lebanese 3.7L build with the V8's larger supercharger. In Summary - hard to maintain grip when changing from 2nd to 3rd....;>) The 3.7L is achieved with block swap from some of the ML350's which had the 3.7L motor - and then you can source some forged AMG V8 pistons to fit.

Probably more for someone who enjoys the challenge and not too fussed about the result - with plenty of time on their hands.