With a 11:1 piston and 95 RON I never experienced any knock. I have read before the ignition advance of the XT 660 is quite conservative so you might get away with 11.5:1 and 95 RON.

But to be honest the high compression piston is only worth it if you consider changing the camshaft as well otherwise you don't get much benefit from it. Otherwise I would try first to replace the rings only.