For anyone that comes here-frustrated after trying many things and using Google a lot-and wondered what the outcome of this thread was, I can't exactly say.
But I can say following Qman's straightforward recommendation with a new radiator fixed all of the overheating problems I had for my '02 Forester that were showing up in conditions like here - long extended highway runs, more in the day than at night, uphill for a while, fine for around the city.