I have like the same laptop of the guy who posted but with optimus. People say here with http://www.amazon.com/Mediabridge-High-Speed-Cable-Ethernet/dp/B0031TRZX2/ref=sr_1_1?ie=UTF8&qid=1382743236&sr=8-1&keywords=High+Speed+HDMI+Cable he could get 120 hz

apparently you can sometimes disable optimus in the bios, but it might require flashing to an "unlocked" bios version which can be risky:

http://forum.techinferno.com/msi/printfriendly1839.htm

i have no idea where the right bios is within that thread though. there is some talk about optimus on page 81

also i'm pretty sure your laptop has an hdmi 1.4a port, but i would double check because when i searched a lot of the info was in french for some reason. there's a lot of conflicting info about whether or not 1.4a can do 1080p at 120hz. as far as i can tell it's not officially supported in the spec, but there's enough bandwidth that it does work.

so if you disable optimus in bios (which will probably require you to flash the bios) and use a cable and monitor that both support at least hdmi 1.4a it should work

No, you can't bypass the 60 fps limit of nvidia optimus afaik.
I also doubt you could get stable >=120fps with that notebook.

In theory both the Notebook and the Benq monitor have HDMI 1.4 which supports 1920*1080@120Hz.

Disabling optimus altogether is possible but I wouldn't recommend it, if you don't know what you're doing, since flashing to a modded BIOS isn't exactly the safest thing to do.

Lol, I already have an unlocked bios, also tried to disable optimus putting in the bios primary display to : sg but it make the screen black after the reboot.

It depends of the games but I upgraded the gpu by a 780m and in one month I will upgrade the 3230m to a 3820qm.

That is weird because if use an external 120hz screen I should be able to set more than 60hz in nvidia panel ?

I am asking because the next plan is to get a benq monitor. Would like to use my laptop as a computer.

as setsul said, optimus will limit you to 60 fps no matter the abilities of an external monitor. unless you can disable it, you won't be able to get more than 60 fps

BenQ XL2411T does not have support for HDMI 1.4. If you want 120+hz@1080 you need DVI DL

You can also use custom timings via HDMI and that works as well (I did it for my planar sa2311w that doesn't have support for hdmi 1.4 and I'm running it at 120Hz right now)

HDMI 1.3 and 1.4 can do 1080p 120Hz, also Display Port > Basically everything else.

That makes sense. But it was just weird because when I plugged my cable in, the max was 60Hz with stock timings.

6 months