Now that I have my doubts about these pumps...I am considering using a pair of IwakiRD30 and running the rads in series for a single loop.

Here's a question: which would work best

Pump>rad>rad>rad>pump

or

Pump>3-way splitter>rads>3-way splitter>pump

Just kicking that around. Of course I could go totally nuts and just get a third Iwaki...but that seems like too much...I am getting excellent flow with the single pump cooler I have now so I am guessing a pair of Iwaki would be more than enough.