Welcome to the forum!
You'll get some great advice here, and some... not so great.
You're average depth of 8 feet, is a good place to locate your diffusers. Putting them at your deepest holes (12 feet) is ill-advised. Reason being, to maintain some sort of thermocline, for fish health.
You mentioned, loudness and energy efficiency. Those things, as you know, make the Hiblow pump a strong candidate, as does your 8 foot depth.
Your pond would do well with 3 diffusers, I recommend the Matlala. The 1" main line run for that length is good. The HD 200 you mentioned will easily do the job. I run the 120LL, and really like it, costs about 75% less to run than the Gast pump, mentioned above. The LL stands for Long Life, it's has upgraded internal components. This summer marks 5 years without a rebuild for me, it's running 4 heads near the depth you should be running yours.
If it were me running a ditch 600 feet, I'd throw a wire in there for an outlet near the pond and locate the pump there. Maybe add a light post down there as well. The Hiblow is outdoor rated and will withstand the elements, although a small doghouse over it wouldn't hurt.
