Everything looks good! Frictional loss is the reason that the Iwaki doesn't hold up as well spec for spec as the mcp355. The more liquid that you try to shove through x-diameter pipe...the more frictional loss. And no it doesn't scale directly...it scales exponentially. The 355 and D5 are excellent pumps with their high psi/head and lower flow rates.
For the final flow check I removed the geo loop from the bridged mcp pumps and PC sub-loops. The res top mcp355 managed a hair over 1 GPM, and the Petra top one came in at .95 GPM. Combined they were a tad under 1.5 GPM.