Following wondra's advice, I decided to check some engines, this is what I found:
Unity 3D (http://docs.unity3d.com/Manual/OptimizingGraphicsPerformance.html)
- Draw Calls: "several thousand" (PC) and "several hundred" (Mobile)
- Vertices: "not more than a 100 thousand" (Mobile) and "not more than several million" (PC)
- Vertices (Developer answer): " if you want [...] to run on low hardwares [...] shouldn’t have more that 100k polygons" (PC), "30k poly" (Android)
- Triangles (User): Renders 5m triangles at 200 fps
Torque 3D (http://www.garagegames.com/community/forums/viewthread/134244)
- Vertices: Around 3 million.
To be honest it was a bit hard to find even this information, I couldn't find anything for Ogre3D or UDK. Even what I found is always surounded by "it depends". So I guess the final answer really is "it depends" but 5m vertices/500 draw calls sound like reasonable numbers to aim for.
I'm leaving the question open because someone else might have better input than this.