Between 120 and 144, no, you won't notice a huge difference, but there is some, and I definitely really enjoy mine. But so long as you're hitting the +100 fps range, you'll notice a *huge* difference over 60 fps and 60 Hz at either 120Hz or 144 Hz.
Your last statement isn't entirely true - the monitor size really doesn't matter as most of the mid range monitors at 120-144 Hz are only 1080p. The refresh rate has no "demand" on your video card performance, the only "demand" is how well the game runs on your machine and if you can hit the high framerates. You maximize the monitor's potential with regards to 120/144 Hz refresh rate as long as you're getting high frames.
ASUS and BenQ both have 27" offerings at 144 Hz. VG278HE for ASUS, and the BenQ XL2720T are both great high Hz monitors, but they're a bit higher in the price range because of their nVidia 3D Vision compatibility.