I have a 600x480 FPV goggles. I want to know if i use a 1200 TVL camera, will I be able to see clearer than if Ii use a 600 TVL camera? TIA.

Does not matter too much. The limitation is the VTX, which can only broadcast roughly 600 TVL max. If you get a good camera and VTX, you will get as clear of a picture as possible. Noise from your ESC and motors will do more to mess up your picture regardless of how good your camera is.