Just a 1-year-later followup... moved to the AZ desert last year, just east of Phoenix. Brought out my '92 245. Driving in traffic with AC on reliably caused the temp needle to climb into the red zone. After some research and deliberation, I opted to replace the 11-year old radiator with a new Nissens OEM type - aluminum core and plastic tanks, not expensive from FCP Groton. I also replaced the water pump, thermostat (cooler one - 87C) and all hoses. I've had zero cooling problems since then. I was reminded of this over the past few days as I was driving at altitudes of 5000-6500 feet, ambient temperatures of 90-100 F, and keeping up with traffic at 80-90 mph (yep, that's AZ for you). The car has also made numerous sprints to Tucson in 110F heat (but closer to sea level), and has been stuck in city traffic at the same ambient temp - all with no sign of overheating or even breathing hard.

Granted, the cooling system is not burdened by the extra loads imposed by an automatic transmission or a turbo. However - my point is that the stock cooling system, in new or well-maintained condition, seems perfectly capable of handling cooling chores in even extreme ambient temperatures.

FWIW, the car is a '92 245 with 175K. M47, VX cam, sport exhaust and suspension tweaks. The only cooling mod is to bypass the AC pressure switch, so the aux fan runs whenever the AC is on.