Bounty,
Based on my own experience with this, I recommend the 180*, and let me explain why:
1. Keep in mind that the 180* setting is reading on the down side (as in the already cooled part) of the radiator, so if you set it at 190 or 195* (what the thermostats are ussually running), basically the coolant will enter the engine a little too hot (hotter than the setting of the thermostat)
2. From what I have found out in my own trial and error, if you set it too low (lower than 180*) the fan will come on a higher speed, meaning no soft starts and thus more amp draw. This is because once the thermostat opens, the temp difference between the setting and the actual coolant will be higher, requiring a higher speed.
3. Again, from my own experience, at 180* the fan will stay off when you are cruising (basically anything higher than 25mph) because the radiator is doing a fine job. When you come to stop lights, it will come on, but will do so softly, and will not run very high speeds, keeping them amp draw low enough that I even ran it with the stock alternator for about a year.
For your reference, I did raise the temp once I was seeing the engine temp rise a little more than I would like (the reason actually was that my coolant was low!), and the fan would still keep off when cruising, but when it turned on, the actual speed was noticeably faster, and you could feel the engine RPM drop a bit and then catch up to supply the electrical power.
Felipe