[Shiraz (Ray)]

The 3200 pixel size would be a good match for your scope in average/better seeing conditions. If you expect seeing down below 2 arcsec and want the best possible resolution, the 694 would be better (the 814 would oversample most of the time - lost sensitivity for no resolution gain).

The 694 has higher overall QE than the 3200 (without microlenses) - they are about the same at Ha and SII but the 694 is much more sensitive at OIII. The larger pixels of the 3200 will give greater sensitivity (but at lower resolution) than the 694, so either chip would be OK from a sensitivity point of view.

Don't get too hung up on well depth - the measure that you should consider is how many "noises" fit in a full well. This is the dynamic range, which is the ratio of well depth to read noise. Most of the chips out there have around 70dB dynamic range - the chips with smaller wells tend to have lower noise and you get the same result as the bigger pixel chips by taking more/shorter subs.

field of view is determined by chip size, not pixel size, as Greg points out. However, your 6MP QHY8 has a much greater field of view than a 6MP icx694, because the pixels of the 694 are smaller - and that results in a smaller chip.

If you get a chip with small pixels, you might consider getting an alternative coma corrector - the MPCC possibly adds about 2/3 of a wave spherical aberration to your optics system, which might just be noticeable at high resolution in very good seeing. There are a few alternatives, depending on the field of view you want.

Can't see reliability of an older camera being much of an issue - my brand new SX camera lasted 2 weeks before it needed repairs. Local support for SBIG seems to be pretty good.

Be careful if you are looking at AO - might be difficult to fit one into the available backfocus at f4