<font color='#000000'>Eric;
Cable characterstic impedance starts to matter at about 1/10 the wavelength of the high frequency of the signal. For example, assuming max frequency signal is 10MHz for component video, then wavelength = 3*10^8m/s / 10^6Hz = 30 meters, thus 1/10(30) = 3 meters.
You should use a true 75ohm coax cable beyond 3 meters which is also well shielded, usually via combo of foil and braided.
For HDTV, cable length beyond a meter should be a true 75 ohm characteristic impedance.
The actual RCA connector is not that critical since the physical connection is only a few centimeters and thus wouldn't have much of an effect at these frequencies. In addition, the form factor doesn't truly allow for a 75 ohm connection, more like 60 ohms max. However, many vendors do offer attempt to offer coax component video cables with nearly 75 ohm terminations and thus it couldn't hurt to use them.
For more info, see:
Cable Budget Guidelines
Component Video Cables: Definitive Guide</font>