I just had mine rotated, balanced and a four wheel alignment on the Buick $55 BTW, for three hours work
My SP5000's in 225/55Z16 on the Buick have about 5/32nds left after about 19K miles. So I'm extrapolating that they would go another 11K miles or right around 30K total life, if driven to the wear bars.
I will probably drive them until October or early November (depending on the forecast) and then ditch them at something near 26-28K miles, as I have a 205/75-14 for the winter on the factory steelies.
TB