The 3-4s is correct. The two propellers are very large so the maximum rpm should be around 6000. The same motor is used for many large 3dlabprint planes so it’s “multi functional” The guy who didn’t get it to plane had added some puppies behind the windscreen with too much weight. He also tried 6s but broke the propeller blades.
I also didn’t get any response for the 900kv/2s setup.
If you watch the video in the c.u Wave Cruiser section you see the recommended setup (4s). I didn’t use full throttle in the video so it does go faster.