My old diesel instructor built race engines for extra cash in addition to teaching.
The point of running a colder t-stat is to allow the radiator to cool the engine during low load sections of track by staying mostly open when a standard tstat would be closed.
In both mine and his opinion, on a stock car or vehicles that don't see track use, have no place running tstats lower than 180F.
The colder an engine runs, the more wear it incurs, race engines don't care as most are rebuilt fairly often. Most low temp racing tstats are at or below 170F.
While the Tstat on these race engines trys to keep the engine at 170F or below, the engine never really drops that low at any point during the race as there is so much heat being produced when the engine is under load, the cooling system size is a science. Because there are parts of the engine that don't see coolant, but do see combustion (such as parts of the head in some DOHC designs) the coolant is desired to have a slightly lower temp in order to more quickly cool these areas.
In your engine I wouldn't run anything cooler than 180F, you are just going to wear out your rings and bearings faster. Personally I run 180F even though I don't get the best heat in michigan during the winter months is because I run a lot of low speed heavy towing in which i'll hit 210-230F on a regular basis, and a 180F operating temp helps cool everything down a bit faster.