Sorry, laptop is out of action so I have no approximator to let you know the results.
However, to date, once you put a G4 in a system then the tubing restriction is almost nil.
Not sure of 50ft though as I've never done that much tubing.
Keep in mind that if the ducted rad can get the coolant temp sub-ambient then the tubing will be working against you as the coolant will heat up again.
Yes, bubbles will tend to collect in the highest part of the system, but I'd put the reservoir before the pump and, if I saw bubbles, just take down the tubing to get it out.
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