You cant compare them - two totally different beasts.
The ST220, is a great motorway workhorse. Comfortable, loads of space, quiet. I have lowered it with Eabach springs, added spacers and added a Miltek Exhaust. The kids love it because it has heated rear seats too
I have had lots of daily drivers, merc's, BM's, Audi, etc - M3, X5, A6, 530i, 730i etc....and I must admit the ST220 is just as good and fun to drive....and A LOT cheaper to service,tax and repair if needed. I picked this one up last January, 4.2K with FSH, immaculate and only 32K on the clock - absolute bargain!