I would definitely go with 12 wks.I never like to run a cycle for less than 12 wks,10 at the minimum.I have never really been a big cutting only cycle guy though either so this is just a personal choice for me.I know there are guys that run "cutting" cycles only and have run shorter ones,but never really believed in them.Your diet and training will determine your results in any cycle so I run accordingly.
If you're running test @ 900mg I would UP THE npp to say 750mg.