Id get a slightly faster processor like the 6400, i dont believe in overcloking as it only stresses other parts of the pc where its not necessary and things can start to break etc, just get a nippy processor out of the box then no need to fanny about with it, thats just me anyway, but no dout someone else will say do it, its so easy, but its up to you.

Graphics card, id say go for the x1950 pro, its a good graphics card for the money, it will play all new games.
Im not sure what a X850XT is( im an Nvidia guy) but it sounds like its old? in which case it will probably make counterstrike look like its on a super nintendo