The thought is for pump 1 to be an Eheim 1048 and pump 2 to be an Iwaki MD20RZ(T). Hopefuly both delivering something slightly less than 2GPM.
My question: Why not run just the Iwaki? Does the reduced restriction( and higher flow) on the Iwaki (no rad) outweigh the heat added by the Eheim? I think not based on BillA's rad flow rate testing.
Comments on this "fan":
http://www.ebmpapst.us/allpdfs/D2E133.PDF
Of course at 55dBA variable speed would be required.