So you've got the bare minimum piston to cylinder gap with the best rings at minimum gaps minimising compression losses. You now need to look at the cylinder head its self, most super bikes now have a "pentroof" shaped chamber, With four valves two inlet two exhaust.
The below picture is what small blobs of potting clay look like when they had the head torqued down & the engine turned over by hand. By carefully removing the squished blobs & measuring with a vernier gauge you can see what tolerances you have left. This was now decked to the minimums achieved through a combination of custom pistons & cylinder head skimming.