My Test PC:
Intel 2,5 GHz Quadcore
6GB DD2 Ram
NVidia GeForce 560GTx 1024MB

It runs faster - each engine with an FPS increase of 200, when not using Normalmapping (except A8, cause we don't use it there right now)

The main Problem of combining entities here is the mapping system. From a 256x256 Block Map, we only show 40x30 Entities max, scroll them with the screen and morph them to another one if needed. There will be 32 different tiles for each room, rockway and hero-room. I calculate with a total of 640 different tiles
i think it's not really possible to morph all them into often used block combinations

we will use a replacer system - like my library example.
Build a 5x5 lib, and 25 Blocks will be replaced by 1 Lib model that covers that space, build it up to 8x5, and all blocks+the lib model will be replaced with the bigger one.