I'm thinking of doing the same to my E420. However, these are my rims of choice!
http://www.bekkers.com/Merchant2/merchant.mvc?Screen=CTGY&Store_Code=BI&Category_Code=morimsevo
I really like the machined finish of the original 15" rims and these polished Evos look pretty close! I'm hoping that 7.5x17 with 215/45/17s won't rub.
My other concern is ride quality. The E420's ride is really nice, firm but comfortable enough (not as smooth as say a new W211.. but...). I'm worried that the 17" rims might make it ride harsh!