Tough one Fred... Real tough..
the 16803 seems the go... but as you say.. is it worth it? its not going to be a cheap move, its not just the camera as you well know, 50~65mm square filters, a CFW, I don't know if your AO unit will support a 16803? I doubt it will though, as SBIG are releasing a new AO unit as a direct result of the STX-16803's larger chip...
I'd assume that the RCOS would illuminate the 16803 well enough to make it viable...
The 6303 as has been mentioned here (and in a previous convo we had a few days back) is good option, cheaper by a long shot too when you consider the STL6303E includes a CFW and your AO unit will still be of use...
As you mentioned in your first post, sensitivity vs mosaic time, the KAF16803 is up there. 4hrs at F/9 will take you 6 hours to do with the ST10 @ F/6.. And the question is, how often do you stop at 4hrs for your Ha? Judging by your gallery, its more like 10~20hrs.. Given that, you're looking at a LOT more time for the ST10 to cover the same amount of sky...
As for Terry's comments re the final image resolution... I really don't think it matters how many pixels the image is.. sure a 16mp camera will chew up HDD space with raw files etc... It all comes down to sensor size or your eagerness to do mosaics. In any case, you're looking at having 4000px wide images minimum, whether you mosaic with the ST10 or shoot single panels with the 16803, sure, your screen can't display the whole image at once without it being scaled to say, 30%.. And yeah, I doubt you're printing A1 or A0 images very often... but there is no other choice, unless you really feel like using an STL1001E, which has a rather large sensor with 24um pixels, heavily sacrificing your resolution, but your 1024x1024 px image will fit on the screen all at once
