I'm a bit confused. I'm looking to purchase varnish, reading here and researching some. What's the difference between Pettit Flagship, Z-Spar Flagship, Pettit Z-Spar Flagship, Pettit Z-Spar Captain's Varnish? I assumed some of these may be the same but when I'm seeing the cans they look different. How do these compare with Interlux Schooner and System Three Spar Urethane?