What is the normal operating temp. range for the Northstar enging in a "99 Deville?

"Normal" seems to vary. I have seen people report 195 - 225. Mine runs 206 in the summer and 213 in the winter.
http://www.cadillacforums.com/forums/showthread.php?t=41490

Mine runs right around 200, at least in winter. Summer is still AWOL up here and I just bought the car this winter so it has never seen a hot summer day, at least not since I have owned it. I would expect engine temp to vary maybe 10% from car to car. Water temp is controled by the thermostat opening when hot and closing while cool. The engine is more efficient when it runs hotter and so the thermostat is set up to hold the water temp as high as possible, short of boiling the coolant. In the old days 180F was standard, now a days it's higher. Car thermostats are not high precision gadgets and so I expect a batch of nominal 200 degree thermstats to vary from maybe 190 to 210 degrees, which means ten identical cars will have coolant temps that vary by the same amount.
Although the digital engine coolant temp reads out to the nearest degree, I doubt that the temp sensor is that accurate. I would expect the temp sensors to vary by 5% from car to car, so if you add the tolerance on the thermostat to the tolerance on the temp sensor, you could have a variation of 15% in indicated temp (30F) from one car to another.
Water temp is OK so long as the coolant doesn't boil. The radiator cap holds 5-15 pounds of pressure in the radiator, which raises the boiling point of the coolant well above the traditional 212F. So long as the car doesn't boil over on a hot day, the engine is happy with what ever temp the car happens to run at.
I only use the temp gage to get an idea of how long I have to wait for the heater to come on in the winter, and as a trouble warning on a hot day. If I see the temp creep up over its normal range, that's a hint that engine heat is beginning to overload the cooling system. In which case I might turn off the air conditioner and back off on the throttle to keep from boiling over. Or pull over and inspect the radiator. It might have got clogged up with bugs or leaves or something, blocking airflow.

What is the normal operating temp. range for the Northstar enging in a "99 Deville?

Mine consistently held at 196 degrees F day in day out, the only variation was in very warm (90+) days idling in traffic with the AC full on, when it would creep up to 215-220 until I started moving again. Once I hit 30MPH or so, it fell rapidly back down to 196.

Sounds like 215-220 isn't hot enough to make the electric radiator fans cut in. I read somewhere on this forum that the electric fans are set for 225F. Which means the Cadillac factory engineers think the engine is just fine at that temp.