If I were you, I would get a 2 stops or 3 stops ND filter and to stack it. From what I read and understand, 9 stops/10 stops are often used if you want to create creative BW shots. Most people use the 6 stops filter more....Personally, I am planing to stack it with a CPL filter with my 6 stops ND. That should give me about 8 stops. I could also stack two long exposure shots in CS6 in order to get the necessary 10 stops+ motion blur effects.
Thanks for the advise.
I considered this option but stacking two filters cause some vignette from ~16mm to ~20mm)
I shall borrow another filter and try again