For now you only have 5-holes pistons (1.3mm holes) and 6-holes pistons (1.25).
On 4WD, some drivers drill them, NJC runs 5x1.4 front with 40WT and 5x1.5 rear with 27.5WT. I run stock 5 holes front with 35WT and 5x1.4 rear with 30WT, didn't tried NJC setup yet.
On 2WD, some US drivers close a hole with CA glue and run with lighter oil, don't know if it is the way to go on UK track though
