there is more soft tubing where you can't see itIf it would have been soft tubing I would have suggested you to put both the radiators in parallel as soft tubing is easier and cheaper to execute. That would give the water more time in the radiators as the flow would have halfed yealding atleast a couple of extras degrees lesser.
the top run is a 3/8 and short one to reservoir is 1/2inch lol.
Currently the pump runs at a very slow 2/5 speed. the coolant spends a lot of time in the three radiators as is, fwiw I am not too concerned about performance since the radiator space I have is more than double of even what some people would call "more than sufficient"