I think for serious work you're gonna want a regulated cooler. From what I've seen of monitoring a single target over a prolonged period of time you're going to have to contend with changing airmass, atmospheric conditions, and temperature. Of course SBIG has an excellent track record, but I'd also look at what QSI has to offer. The SSII might prove useful if you're concerned about budget, but I've heard that although the TEC does reduce thermal noise, the camera has a fairly significant read noise that could cause problems similar to the hot pixel issue of the DSI Pro, probably not as significant, but still something to consider if you're going to try and do millimagnitude work. As an aside, I'm using both the DSI Pro I and II and the II runs much, much quieter than the I both in terms of hot pixels and amp glow. If'n it were me I'd take a hard look at the QSI, but with two daughters heading off to college this fall I'm at least 5 years away from even thinking about upgrading my gear, so for now I'll be sticking with my Pro II.

Have fun looking at new gear!