I think OEM is supposed to be installed on only one computer (motherboard) and that's it. Not to be installed on any other computer (motherboard) ever. Though, you can probably get away with it anyhow, not sure.
I had Win XP Pro 32-bit forever. When I built my latest computer I bought OEM Windows 7 Home 64-bit. Then I started taking some computer classes and got a Microsoft DreamSpark Premium account which gave me all retail versions of Windows for free. I put Win 7 Pro 64-bit on my latest computer, and I put Vista Enterprise on my old laptop but it was incredibly slow. Then I tried to put Win 8 on my old laptop but there was no video driver for it and the graphics were terrible, slow and low refresh rate with the WDDM gpu driver. I then put Win 7 Pro on the old laptop and it runs faster than it did on XP. I put Win 8.1 Pro on my latest computer and Win 8 Pro on my old computer, which I was allowed to update to 8.1 Pro for free. So i'm running Win 8.1 Pro on both of my desktops.
I have none of the problems with Windows 8.1 that others complain about. There is no "new/tile interface" to worry about because I have mine set up to open straight to a desktop just like any other Windows.
The only problem I have with Win 8.1 is that I can't play many of my old games, but I had the same problem with Win 7, and i'm not about to go back to XP. (Nor even bother with a dual boot)
It's hard to say which to get though, but I think people complain too much about Win 8. Mostly people complain because they don't like change. You'll have to move the mouse to the right corner to shut down, instead of the left. (Or just press the power button.) There is no list of programs on the left anymore but the old Start button takes you to the Metro screen the "new/tile interface" that everyone hates but you don't even have to use it. Once on the Metro screen, you just start typing (don't even need to be in a box to type). Type like 2 letters and it will automatically search for the program you are looking for. I turned off all of the UAC so that doesn't bother me anymore. With UAC off you can't use any of the Metro Apps either, but who needs them anyhow.
I would describe Windows 7 as a newer Windows XP. Win 8 is different in a lot of ways but not so different really.