I didn't really consider that. The car only gets hot under load, so yes above 25mph. I could be in bumper to bumper traffic or sitting idling in a parking lot and not have a problem.
Most time, overheating at speed is a flow problem. Get a thermostat with an 1 1/4" to 1 1/2" opening. You could try a good flush, but a scaled up radiator may not clean up without repeated flushing.
