I'd suggest getting your hands on a digital infra-red temperature gun and taking some measurements on the head/intake interface at the water ports, t-stat outlet, top of radiator, etc to see how your actual engine temperature compares to your t-stat outlet temperature. Mine runs about six to ten degrees hotter at the port coming out of the heads towards the t-stat than the temp measured at the top radiator hose. To get my operating temperature in the 185 to 200 range took a 180F t-stat for me.