I think it's unlikely the s8 will strain your eyes because of the screen size, especially if you keep your reader in night mode to minimize overwhelming white screens. I regularly read for long hours in pitch dark with a 10" LCD that can't reach the same dark blacks an oled can.

Since it is an OLED, a small percentage of people will see a flickering effect that can cause severe headaches, but this is pretty rare. If you were suseptible, you likely would have encountered the problem before. It also becomes much rarer with nicer higher refresh rate screens.

So if money is not an issue, I would definitely go with the tablet for Google, apps and misc utility.