I cleaned the tips on my SHO for the first time in perhaps 10 months or so...since last spring. About 7K miles driven in that time. Many of those miles with a mild E blend (15 to 17ish). Have to admit, it was less severe than when I polished them up before, between purchase date and last spring, when I wasn't blending E.
Definitely reduced the soot. But didn't eliminate on my SHO.