I see your point about the gaming. I've only done a little looking into the GPU/gaming connection but from what I can recall Mac GPUs don't come close to a Windows box configured for gaming. I haven't looked specifically at the rMBP. Depending on what games you play you may have to make some compromises. There is plenty of info online to help you decide if you can live with it...
I can appreciate your desire to consolidate your computer usage into one platform. But serious gamers who use Macs tend to have a separate computer for playing games. And there is always the game console route if the games you like are available. One upside to keeping the Windows computer is that you would have a backup computer should something go wrong with the Mac.
Also, I'd like to look at it as a discipline that since it's not the biggest gaming computer, I'll be able to concentrate more on school? Might make some sense.
Yeah the backup desktop is nice to have, but I don't really have anywhere to put it when I clear space for the MBP.