I'm all wishy-washy about which fiberglass to use.
I think I have two or three gallons of epoxy and two layers of 6 oz glass on my Great Auk. It weighs 75 pounds and would've survived all 4 Jaws movies. I can sit it on concrete and jump up and down on the deck without worry. I over did over doing it.

Now I'm building a Mystery, but not as a sunny day racing boat, but as a fast ocean sea kayak for the 2-3 foot 11-14 second swell, no white caps, of Santa Monica Bay. I paddle solo, usually a couple miles off the beach. So I want a tough boat, but I don't think I need another bullet proof kayak (Hillbilly armor 'yak?).
Nick's advice is for thin strips, lightweight lay-up.

I had considered 6oz S-glass on the outside, carbon fiber on the inside. Carbon is too expensive. So now I'm at 6oz in and out, deck and hull. That's probably over doing it as well.

What do you guys think? 4 oz deck (in/out), 6 oz hull (in/out), extra layer in the cockpit area? What's the difference in weight? square foot of 4 oz versus 6 oz?

(I really like what I've read about S-glass 40 percent higher tensile strength. I'll increase compressive strength by adding double curves to the deck (dome) (I'll modify the deck of the Mystery as I did with my Great Auk--no flat surfaces. The increase in stiffness is apparent even with just the wood strips. There's a reason the Pantheon is still standing.)

Thanks,
Will