Fmax is small, please, help me to improve it!

Ilghiz,

I think there is room for one further improvement: the lines

  ScalX2<=ScalX1+(ScalX1>>>SHR);
   ScalX4<=ScalX3+Sum2;

result in two reasonably large adders which probably cause the 'unstable' Fmax result. It would be a good idea to write a module that calculates the sum in two clocks in a split-manner: you add the lower halves of the input factors on the first clock while pipelining the upper halves, and adding these together with the carry-out of the first operation on the second clock edge.

After that you probably can save a few pipeline stages in your module, as you will end up with a few back-to-back registers with no logic between them.