I have both a mono 490ex that I have had for years and performs wonderfully; and a Horizon that I purchased this year and have only had a few chances to use so far, but is promising.
I would say for very long exposure astrophotography the 460/490 is superior. The only limit I have on exposures with the 490 is my patience.
The main reason why I added a Horizon is so that I can have a camera that can do lunar/planetary, EAA, and to attach to a wide field camera lens.
It really depends on how long exposures you can take with your setup. Since you have experience with a Horizon, you probably know that CMOS cameras require a lot more careful calibration images. If the longest exposure you are planning on taking is less than a few minutes, or you are not unguided, go for the Horizon. The USB3 is nice on the Horizon, too.
One of the benefits of Atik is that the 4xx cameras and the Horizon have the same 13mm backfocus and roughly the same shape, so anyplace you can use a Horizon, you can easily swap it for a 4xx. The Horizon does have a slightly larger sensor, but both cameras can use 1.25" filters down to a pretty small size.
From looking at astrobin, you can get great narrowband images with either camera. I don't think you can go wrong.