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The popular term "light bucket" might be apt for visual use with the eye being the sensor, but it doesn't really apply to astrophotography. The camera doesn't see it that way. What the camera does care about is how fast the scope is (F ratio) and focal length.
Most ED80 scopes will be faster - have a lower F ratios than the RC's. This means shorter exposures even though the objective diameter is much less.
Focal length equals magnification. In a visual telescope, we simply change eyepieces to go from either wide field to close up views. However when we shoot deep sky at prime focus, the magnification of the scope is more or less fixed. For the ED80 it's fixed at wide field (Planetary imaging excluded). The RC8 is fixed at narrow field.
This makes the ED80 suitable for large objects like nebula, open clusters and comets, not so good planetary nebula and galaxies which are smaller. The RC8 being narrow field is better for small objects like galaxies, small nebula and globular clusters.
So you see, to cover more objects in the sky, you need both, and we haven't even touched on imaging planets!
Starting with the ED80 will be easier. As mentioned in the above posts, it's more forgiving of guiding errors.
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