ZDoom

Humm... So I'll keep the Zterrain method for now, as I don't know to model yet. Thanks.

A general rule of thumb is: the more amount of sectors/triangles your slope uses up, the slower the map will run. The Doom engine isn't optimized to render things like this. So you're left with choosing fast but very low detailed and jaggy terrain, or slow but smooth terrain.

Personally, I think the best way is to model low-density terrain, bring it into GZDB and the hand-tweak it from there until you can come to a satisfactory compromise between performance and visuals.

I actually find it easier to make my terrain in DB by hand rather than using Terrain Generator: maybe I'm a clutz, but I also find you get far more accurate results.

You're not the first to say that. Maybe I need just more training, for now I just hate my 'outside landscapes', in any game I try to map for. I just can't get they to work, and the Zterrain has appeared as a 'salvation' for me.

I wouldn't mind making terrain by hand and 100% in GZDoom Builder if it somehow supported terrain sculpting tools with variable falloff and things like that. :D