The most efficient way save data from VBO to txt file

Hello everyone, in the first time apologize my english. And now my problem. I have data coordinates x,y,z in Vector3, which are saved to VBO. (load it,view it, rewrite it) and now i need save this data to txt.
I know, that i can use StreamWriter, but what if i have 2 000 000 or more coordnates? Saving time is to long.There is another way to safe large amounts of data to txt file??

//data

 Vector3[] Position = new Vector3[x,y,z];
uint[] VBO_position = new uint[2];

//my sample code for save to VBO:

 void CreateVertexBuffer() 
        {                
                GL.GenBuffers(2,out VBO_position[0]);
                GL.BindBuffer(BufferTarget.ArrayBuffer, VBO_position[1]);
                GL.BufferData<Vector3>(BufferTarget.ArrayBuffer, new IntPtr(Position.Length * Vector3.SizeInBytes), Position, BufferUsageHint.StaticDraw);
         }

Thank you for any help
(need more information)??