Quote: "it's size (scale) doesn't matter so much really, more importantly is it's number of polygons and the size of the textures. also DBP handles multiple limbs on an object easier than multiple objects, most of the time."
There is two extra problem to consider with scale:
-If the scale is too small the camera would clip the object too early.
-Likewise a too large scale is not good for array and position handling as well as increased chance of Z fighting.
As for Polygon counts, DBP uses the back to front space rendering with the volume of a pyramid. In short, all object within the field of view and in the camera's range is drawn, starting with the objects at the back (furthest from the camera) to the front.
This means if you were looking at a wall in the direction of the main area of your levels the wall might only be 2 polygons but the rest of the level within this volume will be drawn first before the wall and this is waste of rendering time and your fps will be lower than expected.
You'll either have to design your game to use the field of view pyramid effectively (reduce the unit cubed volume of the rendering pyramid) or code an culling function into your game, if your level size becomes too big. For smaller levels this is not much of a issue since the fps will still be very high and there might not be much to cull off anyway.
As for textures, everything is drawn on a per-pixel bases, the only time compressing your image becomes effective is in the memory consumption.
with this said its more about the total amount of pixels drawn to the screen at any one time and how long this takes, and this is determined separately from the polygon limit, and is known as a fill rate.
In theory many small textures are just as fast as a few large textures, if the total pixels passed to the Gpu are the same.
But DBP uses a number of tricks to speed texture drawing up as well as control and handle texture size to screen space with the help of mipmap and texture sorting* (*If enabled)
Mipmaps are basically small copies of your texture with the size half for each texture, the good news about this is that it reduces your total pixel count for objects where it would be impossible to make out the pixel of the texture on the screen and its automatically on by default.
Texture sorting is available if you use the "Texture object" command and it basically renders in the order of the texture ID, so everything with the same texture is render together, this can be use if you know a particular groups of objects will be drawn is a fixed order: i.e. a 3D Heads up display in game.
