gorgesailor said.. What do you mean by too fat? Generally speaking the PT type screw calls for a hole roughly 90% of the thread O.D. The screws with larger core diameters are stronger, so there would be a trade off & it is unlikely you would need the more open thread design for footstrap inserts as they are usually made from glass filled Polycarbonate or other dense engineering grade plastics.
I think it is much less than that
The PT stuff for windsurfing has been M6 with a minor dia of 4-4.2mm for many years. That's more like 66%
I drill my inserts to 4.5mm so there is good engagement but they won't split if there is a tiny bit of sand or salt residue in there
Inserts are not glass filled its just thermoplastic so does need PT
I agree Torx is BAD as when it is too tight the driver does not cam out (pop out upwards) like Phillips and Posi does.
My only issue with footstrap screws is since we went from normal self tappers in the late 1990's and Cobra started using the correct thing (PT / Plastite/ thread forming screw) now there is a monopoly and you just can't get them at a decent price. Unless you order 500 from screwerks ......