The input lag on either of those listed is not fantastic. Unless you are sensitive to the motion of 60Hz screens then I would probibly try and get the lowest response time screen that you can.
If you are talking about having a machine to run at 120 FPS in CS, I take it you are already using the CPL mousefix tweaks, running the mouse at 1000Hz etc?
you can see here the Asus MS246H gives only 6.9ms "input lag" on average. The Acer you detail (according to this http://3dvision-blog.com/tag/acer-gd235hz-review/) has around 15ms input lag extra then the Viewsonic, which has 14ms according to the graph.
If you analyse it on a frame by frame basis, the time taken to show something new on the screen could be 6.9ms + 16.7ms = 23.6ms on the Asus.
Contrast this with 14ms + 15ms + 8.3ms = 37.3ms
IMO going to these high end 120Hz screens doesn't make a great deal of sense for the moment *unless of course the 15ms figure is wrong*.
If you can feed 120fps constant to the screen then you will get better motion from a 120Hz screen, but there will be a lag between things. With the 60Hz screen, the lag is very small, but this is increased with the near stone age 17ms refresh time for the screen.
Down-sides to both technologies, but I would say for serious gaming you should be fine with both, they both have their own merits. If you can put up with 40ms lag, which is nearly 2 whole frames plus input lag for the Asus, then go for it. Once the 40ms lag is "gone" (by this I mean the lag has and is still happening, it will not be figured in for every frame), you will get a refresh every 8.3ms which should make the movement smoother.