Technically the SL-5500 screen is only reflective and it only has a frontlight, not a backlight, which is why it works so well outdoors. (Transflective is both transmissive and reflective and so has a front and back light, giving it excellent brilliance indoors and also works outdoors)
The C7x0 on the other hand only has a transmissive screen, so only a backlight, but that means it doesn\'t work too well outdoors, yet is very bright indoors.