Just came across this thread from Google search (incidentally, though, I do play TF2).

My setup is 144 Hz + 60 Hz. Dragging windows (no pun intended) is laggy on the second monitor. Some applications (notable, Chromium) suffer from extreme input lags when on "slow" monitor. And turning Aero off does help.

I play games on primary (faster) monitor full-screen, and no problems with them so far.