I'm sorry to be so slow in acknowledging your response. I didn't get an e-mail notification of the response (not sure if this site does that), and I just wandered back to this post as I'm ramping up to start attacking this issue.

I lucked into a flowmeter at a good price, and I'll be installing it in the next few days. That will give me an idea of existing flow rates, high/low, with/without heat pump. I'll probably go ahead and calculate the head. It will also take me several days to digest all the good information on your Energy Efficient Swimming Pools site.

If anything challenging comes out of this additional research, I'll post again to this thread.

Thanks!