heightmap landscape ... what kind of resolution ?

I’m trying to re-invent the wheel, doing my own terrain rendering based on a heightmap.
I’d like it to be versatile enough to serve in an RTS-type game, but also in a FPS-view (no quake, more like a first-person Scorched Earth).

For comparison with other games and programmers, I’d like to know of all you world builders, how large your patches of land are, and how many pixels you use for your heightmap. A pixel per virtual square meter, a pixel per virtual square kilometer … ?

For wurm online, we have maps of 40964096 tiles. Each tile is 44 meters.
We use world machine to generate the base heightmaps, then process them through a custom tool to plant all trees and so.

Thanks!
I’ve admired the landscape in Wurm Online before. I’m definitely going to take a hard look at this world machine.