i am having a similar issue but its normally when i sit in traffic for 5 mins or so (with or without ac on). the needle slowly increases beyond 210 but with ac on a tad faster. when i start to drive, the temps would decrease slightly and normalize above the 1/4 mark.
I have replaced the water pump, radiator, and thermo two years ago. Did a semi radiator flush (upper/lower rad hoses blew), changed fan clutch 3k mi ago, cleaned the radiator as well as the condenser. does not use oil or coolant.
I thought about going electric as that would definitely cool in slow to stopped traffic. but i want to be sure nothing else is wrong before spending the $$$