I had the Sumitomo's on my 330i, and I have S-O2's on my 911.
The S-O2's (previous generation) are pretty sticky, even more so than the Sumitomo tires were. Since I am going to replace the tires soon, I will go with the S-O3's on the Porsche because wear is not a concern of mine.
I bet the Sumitomo's will last about 30% longer than the S-O3's, but they are less grippy. They are also only about 65% the cost.
If you track your car, or autocross, and ultimate grip is essential, get the SO-3's.
If you drive hard, fast, and enjoy taking corners on the street (no track use), I would get the Sumitomo's in a second. They are an excellent tire with few rivals. I never reached the limit of my Sumitomo's on the street (you shouldn't be doing that anyway).
Personally, I think the S-O3's are overkill for the street.
