I'll probably be getting a QSI 683WSG-8 soonish here. It's an APS-C sized sensor, the KAF-8300, full mono, with an 8-position filter wheel (LRGB, Ha, SII, OIII and unfiltered), off axis guider port, and has a perfect gaussian read noise distribution. It's a very expensive camera though (with the filters and the various necessary adapters for use with my Canon lenses and standard telescope equipment)...about five grand. So I won't be buying any other cameras any time soon...least of all Canon, Canon sensors, even their newest ones, are just too darn noisy with poor noise characteristics.
I purchased the 583WSG with the 5 position filter wheel a couple of years ago. The QSI cameras are incredibly well made - there was a lot of nice design work that went in, unlike some other CCD cameras that feel like the mechanical design was an afterthought. I wish that the 8-filter wheel was available when I purchased mine, but I'm interested mostly in galaxies anyway, so the 5-filter wheel is fine for now. I purchased it when I had the funds but little time, so I've used it much less than I would have hoped. But I'm planning on building a ROR observatory in the spring and now have more time to dedicate to this hobby, so I hope to start getting my money's worth out of the camera at long last.
I did a little AP using the 20D before I got the QSI camera. Not having to combine the LRGB data was convenient, but there is really no comparison between the DSLR images and the CCD images.
And FWIW, I just tried the free PixInsight demo with my most recent image. It is really difficult to get my head around it, but the results are better than I could get with Nebulosity + Photoshop. But, I am a novice at it either way.