Thanks Kevin, all very interesting! The 5:1, 3:1 and 2:1 formulation issues was something new to me and might explain why some are more sensitive to e.g. WEST (5:1)?

For the peel ply I am uncertain. Your opinion weights heavily as you have loads of experience. Others, especially the amateur aircraft builders, say to sand anyway. Did you get your information from the cloth/epoxy manufacturers or through experience? I know the epoxy manufacturers said peel ply removed the need to sand, but they pulled that statement back as far as I have heard?
At least I now know to wash and sand thoroughly if I use regular nylon as peel!