The RC4 quick release plate is HUGE - designed for much larger cameras than the Canon EOS system. The RC2 system is much better suited to EOS cameras and their related lenses.
You may find the 498RC4 at a lower price than the 498RC2, but that's because the 498RC4 just does not sell well. Don't be hooked into buying one, as you'll be unhappy with it. In order to make a quick-release system work well for you, you want to keep the QR plate attached to the camera at all times. The RC4 plate would get in the way when you're hand-holding the camera while the RC2 plate won't be in the way.