I don't think anyone's going to argue the point that a rougher sanded piece of wood will hold epoxy with greater strength than a fine sanded one. It absorbs the epoxy deeper and gives it more surface to grip. The coarser sanded wood will wet out noticabely darker than the fine sanded piece. If it's too coarse, even if it's sanded with the grain, sanding marks may show.

So - you're trying to balance adhesion, wood color and eveness of color. I sand my kayaks (strippers) with 100 on the outside with the grain and not only like it but trust the results. I sand the inside with eighty and even 60 would be OK where it doesn't show. The inside gets noticabley darker and absorbs more epoxy, but it's never coming off. 120 on up is too fine and denies the epoxy a good grip. It will look fine and act fine untill it gets stressed.

If you do some tear test, you'll find, what I'm saying is true.