Peter 16 is a good number I have found. I don't use median on my darks I use sigma reject mean. That gives a really nice dark for subtraction and I guess my results show that.
You're right about the filters if they use a larger sensor. However, I am sure they will come up an elegant solution. This camera is very light and nothing like the weight of an FLI setup and filters.
Fred, I would go with a larger sensor too, but for now this size sensor suits my imaging interests. I always thought the 6303 sensor with it deep wells and size was a good size for 2.7" focusors. The cost though is usually much higher than even the 11000 sensor.
Greg QSI have had plans for the 700 series and published this on their site for as long as I have owned my QSI. Sometime in the future (when that it, no one knows) I guess they will get around to completing the design. I would not hold your breath though.