Don't you actually need to buy a new license? I don't think you can activate any 3rd party installer (say downloads via microsoft.com, making an usb key) with the oem serial? Not sure though, the only windows license I'm currently using isn't OEM, it's a full 8.1 pro license.

This does sound like a good argument for wiping the OEM windows 7 pro partition on my laptop, and install a windows 10 trial or something (I currently just run Debian GNU/Linux on it -- but it's technically dual-boot).