The stripper I most paddle has 4 oz cloth with the extra football shape or additional 4 oz on the bottom and I beat the boat regularly. I don't seal launch from rocks or crash land into rocks but have accidentally landed on them in mild surf. The 4 oz layup is what is most commonly done by strip builders who use their boats to the fullest. Years back 6 oz cloth was the norm but nowdays everyone seems to be fine with 4 oz with the extra shape on the bottom. I put an extra layer of 4 oz on the floor of the boat from the seat forward because of abrasion of sand etc.

If you were going to do a circumnavigation of Australia with an extra 70 lbs of cargo and doing huge surf landings with no support team, then maybe go with the 6 oz heavy layup. Other than that, the 4 oz layup will server you fine. Besides, the kayak is not going to fall apart. If you do scratch through the skin because of some freak accident, you fix it and go on.