The shrouded 2 fan set up is restricting airflow when you have the fans turned down, thus running hot at all road speeds.
When you turn the fan speeds up and it cools down to 185* that means that your radiator and pump combo have enough cooling capacity to do the job.
You dont need a new radiator if you can cool it down to 185*
I would overdrive the water pump with a different pulley ratio and add a Hi flow thermostat to take advantage of that capacity and run the fans full tilt all the time.
If you choose a new radiator put in the biggest 2 core you can find. IMO Griffin makes the best USA made radiators, they are great people to work with and know cooling systems very well - no guessing games.