OK!
My experience is this. I live in Kanaduh!! and the requirement is high temp. for winter and low temp. for summer. Those four bangers run very hot..particularly in the summer. Therefore, if you run the higher temp. thermo you might possibly run the risk of overheating especially in the summer. In general, the cooler you run the engine, the more life you will get out of it. I know the winters are mild in your part of the country...been there...loved it.So for me, the winter is very cold here..I need the high temp. thermo if only to get heat in the cab. But in summer I switch to lo-temp. You might be surprised to know that it gets very hot here in the summmer ..100F plus on the worst days...and very humid. My best advice would be to use the low temp.
Now..regarding the emissions testing....my experience has been to run the engine hard before testing...get it good and hot....a nice fast highway run and straight to the testing station. Use good quality gas as well and maybe some "emissions pass" additive if you are a little nervous.
Overall, if the engine is hot and in good tune when it is tested, there should not be any problems.