The high refresh rates you see advertised by TV manufacturers is largely a marketing 'gimmick' that has more to do with backlight scanning and 'percieved' quality than any real refresh rate numbers.
Irregardless, your actual refresh rate on your tv is going to likely be capped by what your pc is going to be able to deliver: Even if your video card is capable of sending 120Hz to your tv's, you're likely not going to be generating 120 fps out of FSX. If you cap your frames per second at 30 (as is common), and your video card is sending a 120Hz signal to your TV which is in turn displaying it at 120Hz, it's simply going to be redrawing 4 identical frames in a row for each frame.
In essence, there's likely not even a really strong need for 120Hz TV's if you're only using them for FSX/P3D.