If you're doing professional video editing then you need IPS for "truer" colour and image quality.
120Hz isn't supposedly perceptible by regular humans. Apparently we can't really see above 30Hz. B.S.!!!!!!
Anyone who games a ton, especially fps gamers, will be able to tell the difference between 30 fps and a solid 60. Above 60 it just makes it look smoother unless u have that adaptive vertical sync. With the new adaptive vertical sync it can make your 60 fps games just feel 120 fps smoooooooth.
I would suggest the best of both worlds; get the IPS monitor and then get a new gen nVidia card, or wait till 120Hz ips comes out!!