Hmm... it depends a lot about what games you intend to play. There's games which don't work as good with Windows 7 as XP, but that's also reversed. Thinking about the term "modern games" I see that your graphics card will limit your possibilites to play them if they were to require DirectX 11.
I think that if you play older games, Windows XP is the best choice, but then we go off your topic about modern games.
So what games do you play?