Sorry for late reply, but I thought I should post for whoever might have this same question.
For me, the game is running well on a GeForce 730M - the key is to lower your resolution. I always run fullscreen 1280x720.
One time I connected to a TV and it went up to 1080p and I immediately had issues. Bringing it back down to 720p I can even do 4 player split-screen OK.
I had a similar experience with TF2 even though it is quite an old game. It started running really poorly all of a sudden and I started turning down graphics settings to help. It didn't help and I was baffled. The difference was that I had used an external monitor and it bumped up to 1080p. After I went back down to 720p I could turn the model/texture quality back up with no issues.