Hands down the C9.25 EdgeHD! My friend and I operate a C11 EdgeHD at native F10 and John Hayes operates a C14 (I am not sure if it's an EdgeHD or not). Many remote observatories operate large telescopes and with good reason. You have excellent skies to take advantage of. Once dialed in, this should give you fantastic results. I would not even bother with reducing the focal length or make it faster. In a remote setting, you have time by your side. Image fewer targets, but go deep. The idea really is to nail the deep sky stuff.
The target lists should include Abell, planetary nebulae, the smaller galaxies, etc. - those targets are difficult from the backyard and difficult with short to medium focal length scopes.
Not that the TOA will be a bad scope (in fact, it is a really good scope), but it will limit you in taking advantage of the skies. You just can't produce results with it like what you can with a long FL scope under superb skies. I used a 5in APO for about 15 months at my remote observatory and found the results very limiting - and mind you, I tried going deep (as in total hours, but it wasn't worth it with a 5in APO).
BTW, if you are worried about flats with the larger scope, you should not. There are plenty of options - sky flats will work. However, if they don't, you can get the FlatMan from Alnitak (it needs to be wall mounted) or you can get SnapCap from Gemini Telescopes in Europe. That works very much like Alnitak's Flip-flats (unfortunately, Alnitak/Optec don't make those for larger scopes any more), so it will act as a cover for the scope and allow you to take automated flats as well. The FlatMan is more cost effective but you will have to spend some time to determine the exact location and how far you need for it to be, while the SnapCap will really just fit (ensure it is well centered and does not move during operations otherwise your flats won't work), the downside is that you have to order it from Europe and is expensive.
Lastly, if in the future you feel like doing wide field, you can always piggy back a small APO on top of the SCT - the AP1100 won't break a sweat. But honestly, wide field is for backyard (mostly narrowband anyways), so I wouldn't even bother with something like that.
Edited by dhaval, 14 August 2019 - 10:40 AM.