It will run TF2 fine, CS GO maybe if you turn down some settings.
Those games, especially TF2, are CPU-bound. I had a sandybridge i3 at 1.4ghz and it ran TF2 like crap (30-40fps which is not good for online) when paired with a 720M, meanwhile a 9500GT DDR2 (a slower card) ran that game at 100fps when paired with an i3 at 3.3ghz.
The fact that you have a 8400, I guess you have an AMD apu, which might be similarly lower clocked. Try TF2 and see, it's free and you can turn up the graphical settings except anti-aliasing (if aliasing bothers you just force MLAA through Catalyst). Make sure you enable multi core support in the settings.