Personally, I think the oil/coolant circuit is inadequate for a turbo motor on a stock size radiator. It's likely your coolant system is fine (assuming you're not overheating), but the additional oil thermal load is exceeding radiator thermal capacity. I run an auto tranny and switched the ATF cooler from the radiator to an oil/air cooler for this exact reason.
T-stat wise, you want to run a stock temp stat, either OEM or a Stant Superstat. For where you live, you can use a 180 deg stat, but do not go any lower. Test the stat in a pot of boiling water for correct opening temp and remove the jiggle valve before you install.