If you are planning on gaming on 120Hz monitor, overclock your CPU is a
MUST, if you really want performance. As for your components, I don't see why it can't overclock, unless your i7 is not a K-edition CPU. If you got a i7 K CPU, you just need to get a decent CPU cooler, and you are good to go on overclock.
If you really really can't accept overclocking, you simply won't get as much benefit from the 120Hz monitor as it meant to be, and the chance are the graphic card(s) will get bottlenecked (meaning that CPU holding back the graphic cards i.e. 40-100fps CPU holding back 90-180fps+ graphic cards). So rather than trying to push for 120fps and fall short by a long way, I would suggest you consider getting a 2560 res 60Hz monitor instead. Personally, I would give one of those ultra widescreen 21:9 2560x1080 res monitor a go:
http://www.overclockers.co.uk/showproduct.php?prodid=MO-063-AS&groupid=17&catid=1120
http://www.overclockers.co.uk/showproduct.php?prodid=MO-066-DE&groupid=17&catid=1120
So for your FPS games, while it won't get the benefit of smoothness, you would at least benefit from the wider field of view and offer you advantage in a different form.