I think you'll find that the only cinema screens that are 120hz are actual 3D panels which can run up to £1000.. maybe a little cheaper.
Cinema displays that say they are 120hz that are not 3D panels are just using a buffer type technology that inserts a frame between the frames of 60hz, which isn't actually 120hz, its just fobbing you off with tech wizardry..
So yeah, you could get a cinema display... but do you really want to be sitting that closely to a 40inch cinema display... maybe you do!!... Just make sure you put sunglasses over your 3D specs!!!