The 5" piece of Beech Flooring is what a cupped board looks like before planing. Much of the imported prefinished wide plank flooring has moisture issues. Better to rent a moisture meter and check the ends of the boards for moisture content before putting material down from another part of the world. If it is more than 8% consider returning it for a refund. We have seen prefinished flooring measure at or above 12%.
I was skeptical when Merv told me that I could put down 1x8 boards without surface nailing or screwing--however it is true. When flooring is dried properly it lasts beautifully.