
So now to the idea... Not just how big it is, how to make it small?
I mean some geometry + TM can pre-tessalate it + pre-defined objects(like ceiling or I dunno now... grass? terrain? eh..) = pretty small geometry
Bbbut: 4-6 pairs of textures? Plus specular maps, bump maps... Random maps

Well that's some sorta big... Don't you think? Well, maybe pre-installed textures? Oh come on! That's boring. Therefore we have one technique:
Pick up one small texture(64x64) + put on "difference map". You basically repeat the same texture, and then put on the same texture on it. That's kinda useless on so called "colo(u)r maps". That's basically the thing you see.
But, in a game called fuel the devs used it on bump and elevation maps. And achieved 14,400 km² game world. That's kinda awsome, right?
So these are my thoughts about the custom block size.