Simon,
If it were me I would use a Batt lap. Combination would be Batt + 100K for your competition stone. I get excellent results with this combination on Quartz. Flat facets and a great polish. But that’s just me. I haven’t used some of the newer laps out there and the results from them may be just as good. If you don’t own a Batt, you should.
W@rd