How cool is too cool?

I've done my annual cooling system flush and fill and to get ready for winter.I dropped in a mr gasket hi flow tstat(195*) and my temps are def lower.....it's runs right at 180-200 degrees and I rarely have to turn on my dual fans.I haven't noticed any increase or decrease in mileage but wonder at what temp would the 4.0 be happiest?
Am I risking any damage or excess sludge formation running this cool?Should I switch back to the factory stat that warmed up a lot quicker and constantly ran at 205-210?
Initially I thought this mr gasket stat was stuck open but a pan of hot water shows that the stat opens at 195

Normal temp is 200-210. Stock gauges are not reliable.... You should be fine though.

with winter around the corner, I'd put the 195 Tstat in.
Since you don't have any overheating issues, running the 195 should cause no problems.
As for the normal operating temps, It's 5-7 deg swing from whatever the Tstat's deg is.
Mine runs a very consistent 196-198 (no more then 206) and seems to love it, resulting in 23 MPG and no problems.

Temps were read from my auto meter gauge....I stopped trusting the stock gauge years ago when I first had an overheat