Well it can handle 512 512 512 maps and they are 134,217,728 blocks.

And it does that with physics on and everything.

They are not exactly Entities like your game instead they are just data in a multi-dimensional array that gets converted into vertexes and displayed on screen.

It handles 134 million with no problems at all the only problem was the LOAD TIME for such a big map since it uses ushort instead of byte the time it takes it 100% longer than an equivilent minecraft map.