to me if your cars going fine with daily-driving under 5k-rpm then i would be considering changing your radiator, or at least get it pressure tested in the car.

I have a B16a in my CRX and it always ran stupidly cold, after a year of having i finally checked the thermostat and it was stuck open, got my radiator checked and it had a cracked core, possibly due to the faulty thermostat.

Just my 2c