when you reach the upper rhelms of 230' and above your risking head gasket failure. i understand pontiacs run hotter but you shouldn't exceed 210' in normal climate and operating conditions. if you live in hotter weather add 5-10 degrees for the sun baking the engine and stagnant air. there are some mods you can do to the water pump to get it to flow more but like others said you should check the lower hose to see if its collapsing. at this point im saying its a flow problem because the hotter you get the less coolant gets to your engine and the faster the temps rise.