I would seriously consider an Edge 8 inch with a focal reducer. That makes it a 1500mm F7 scope with a flat field. add a moonlite to it and add autofocus and you are home.
I just could not get decent results with the RC. It was a constant fight with collimation, longer exposures which you need with that scope were a nightmare. Your mileage may vary. There are people who are happy with it and are taking great images, so it's possible.
Don't forget that with the RC you will need a field flattener, a tilt plate and also if the stock focuser is not up to it a focuser upgrade.
You can add defraction spikes in post processing if you really like them!
I have a 6" RC that is great fun to image with, except for the focuser mount issue that's been discussed above.
I would love to replicate the 1260mm focal length of the 6", but with very good mechanical quality. I decided to take a chance on the EdgeHD 8" with a reducer. It has been a decidedly mixed bag.
I started with an Optec Lepus reducer at .62x. On paper, it should get me to 1255mm, which is perfect. The reality is that, even with exact spacing between the reducer and the imaging sensor, you need to adjust the main focuser on the SCT to reach focus. In the process of doing so, you end up increasing the focal length to about 1450mm. This would not be a huge deal by itself, but when you get the system to reach focus, you've moved the primary mirror enough that it's spacing with regard to the Edge's internal corrector is such that you are no longer getting optimal correction across the entire imaging field. With this configuration, stars in the corners of my ASI1600 are slightly elongate. The aberrations are not particularly large, but I really wanted correction across the entire field.
I have located and purchased one of the hard-to-find Celestron .7 reducers for the EdgeHD 8. With correct spacing, it should get me well the well corrected stars that I am looking for, and should get me 1422mm focal length. I've somehow ended up making a bunch of configuration changes with my mounts, and the weather has not been great, so I've not had a chance to test with the Celestron reducer yet, but I have high hopes that it will work as advertised.
In all cases, you should be aware that for good performance, you will need to use an off-axis guider to be able to do exposures longer than about 3 minutes. Much longer than that with an external guide scope, and differential flexure due to the movement of the primary mirror becomes objectionable - even with the primary mirror locked. To be sure, this is subjective. I found that I could live with 3 minute exposures (although I wasn't terribly happy with the slightly elongated stars). At 5 minutes, I just through the data away as I considered it unusable. I spend an entire night of testing with swapping out guide scopes and different guiders to prove that the problem was with the OTA and not any guide scope, the mount, or any bracketry that connects everything.
And the final complication is that, for the 8" EdgeHD, both the Optec Lepus and Celestron reducers require 105mm of spacing between the reducer and the imaging sensor. This is precious little to work with once you add an OAG into the mix. I was able to get it to work with my Teleskop Express Thin OAG. I also have a Celestron OAG, and it's not even close to fitting into the available space. I also have an ONAG. It can (barely) fit with the main sensor, but to get my guider and main camera parfocal, I have to push the main camera back a bit, which takes me out of the 105mm spacing again. This means that the ONAG is a non-starter with the 8" EdgeHD (it should work with the 9'25" and up Edges, since they have significantly more back focus with their Celestron reducers). Also, I like to use a camera rotator when I use OAG, so that I can pre-select a guide star and automatically position the OAG to land it on the guide sensor. There is no way to get a rotator to fit into the available back focus with the OAG on and 8" EdgeHD.
I'm certainly not giving up on the EdgeHD. I just wanted to point out that there are compromises with it, as there are with anything. It has very good optics and is a great all-around scope, but has some limitations. I'm going to see how it goes with the OAG with regard to guide star selection. I've already tested in star-rich fields and demonstrated that I can guide for as long as I want with round stars (I tested up to 30 minutes on a single exposure). And my mount is good enough that I can go with really long guide exposures if necessary to get a guide star. 60 second or longer guide exposures are no problem. The limit on guide exposure length is actually that primary mirror movement again.
If I find that I really, really need to get a good setup going for that 1260mm focal length, I'll probably end up with a 5" APO refractor at some point in the future...