I have the same JE 12:1 pistons and the same crappy gas options. As getting (consistently) high octane fuel became increasing difficult in WI and converted the bike to just run on 93 E10 or higher. the mileage sucks but the detonation problems went away as well.
I have looked into the bores several times and so far all appears well (borrowed a bore scope from work).
FWIW when I assembled my motor I took a file to the sharp edges of the piston domes. That may be helping in avoiding hot spots.
05 speedmaster - 1100cc, 11:1 racing pistons, Carillo rods, thunderbike cams, ported and polished head, 2mm over intake and exhaust valves, Barnett kevlar clutch, scepter pipes, oversize manifolds, 45mm HSR's, TTP stage 4 firestarter
| 
