Good article. We have a 2013 M5 Sport, with automatic transmission. We ditched the OEM 205/55-16 tires (Toyo A20s) at about 18,000 miles. Slipped from dead stop under dry conditions, and slipped in wet conditions under many conditions. I felt these were just unsafe and replaced them with Hankook Ventus S2 Noble S2s. Much better overall traction, but I managed to spin the tires once from dead stop on dry pavement one. I think the M5 is too light a vehicle for the 205/55-16s, which may be too wide. Maybe a 195/55-16 will be better the next time around for more ground pressure (and more friction).
Overall, its a versatile car for a very good value, and we like it alot. A bit noisy on the highway and lacking in some amenities. I'd also be interested if you tried adding Daylight Running Lights, as the Sport version did not come with these due to another cost cutting measure.