to Ice in Space Leon!
All Edge HD models have a flatter field than their equivalent non-Edge HD model due to the field flattener in the baffle tube.
According to Celestron's Edge HD white paper (your favourite search engine should find the PDF), the Edge HD 9.25" has the largest imaging circle, and the 11" and 14" are just sufficient for a full frame DSLR sensor.
The only problem is that currently there is no reducer (from Celestron) for the 9.25" model, unlike the rest of the range, so you'd be limited to f/10 or an alternative third-party solution.
The Edge HD 8" is only suitable for APS-C sizes sensor as the baffle tube is only 38mm in diameter. It is however the smallest and lightest of the range by far.
Using your 800mm setup on an equatorial mount is a good place to start, although maybe try without the teleconverter, and or any other lenses you have, as at this time of year the Milky Way rising is quite a sight
But anyways...what are your objects of interest? That will really give the best determination of which scopes would be most suitable for your interests, as telescopes are just like lenses, different focal lengths for different purposes.