Dividing speed and page0 problems

Hi,

I have some questions about the compiler:

1) I want to divide a variable to 2000 as fast as the STM8S microcontroller can. Is there a difference between the statements below in terms of speed?
    x = y / 2000;           
     // and
    x = (y >> 4) / 125;   // (y >> 4) is equal to (y / 16)
2)  Is there a difference in terms of speed between dividing a variable to a small number or to a big number of same type? For example:
    a = b / 1000;        //1000 is short
   // and
    a = b / 2000;        //2000 is also short

3) I have a problem about page0 keyword.  The code is like below:

  static page0 signed int VariablesArray[3];
  static page0 signed long SumOfSquaresArray[3];
  ...
  ... 

  for(a=0; a<3; i++)
  {     
     SumOfSquaresArray[a] += (long) VariablesArray[a]  *  VariablesArray[a];
  }

If a define SumOfSquaresArray in page0 like above, I see that the multiplication process does not execute. But if I remove the page0 keyword from the definition of SumOfSquaresArray, the multiplication executes successfully. 
Instead of using SumOfSquaresArray, I used 3 different page0 variables and I saw that multiplication executed successfully.
If I use a page0 pointer instead of using SumOfSquaresArray, I see the same error.

What is the cause of this unsuccessful multiplication?
And I also want to learn whether I can define a pointer in page0 or not?

Thanks!