Generally with hardwood decking, you want to make the holes bigger than the shank of the screw by +1mm, to allow the boards to expand and shrink. Ipe is a very strong timber, and when this isn't done I have seen it snap screw fixings.
The fixings should be 2.5x the thickness of the board in length with such hardwood's, as the pull out force if they try to cup is immense.
clip fasteners should be used with care, there are many different types, and you need to ensure you use very strong clips with dense hardwoods so that they can resist any cupping (the cheaper metal ones bend, and plastic ones can snap).
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