I didn't got to the 4mm yet for 2 reasons. Knowing the location of the carbon fibre and the width of the body mounts, if I went with the 4, the 2 screws that hold the shock tower/body mount on would probably stip with the leverage that the 4 would produce. The 3mm was almost 45% stronger and still had some flex. Also, I put another screw in the top of the rear bridge so I have 3 screw holes in the rear shock tower, the pic does not show that.
Thanks for the question