EDIT: Haven’t found the source. I did find that the existing ViaSat-1 latency (on Exede, and actual ping times not satellite->ground latency) is 600 to 700ms, so that’s roughly in line with what you said. Exede do a bunch of latency compensation where they can so people often report lower latency, but for eg online games that obviously won’t work.

I also know that what I read before was specific to airplane in-flight internet, although I doubt commercial flight altitude make any difference to latency, so that’s likely an irrelevant point.