Most of the pitch effect s in the GT-10 are not polyphonic, but the closest is the "Pedal Bend" effect which can do polyphonic notes (playing more than one string at a time), but you will run into problems with strange harmonic 'anomolies'.
As well as the VG-99, there are dedicated 'drop tune' pedals out there.
I have a couple a things to add to this. Floyd rose trems are a nightmare, in my opinion. If one is hell bent on using them, I believe there is a device that attaches to the back of it that allows one to keep it stable during string change. Kahler is a much better system. As far as drop tuning, I recommend get your hands on a Ibanez or Schecter fixed bridge. The Schecters are more bang for your buck compared to Ibanez Rgs. Dedicate one axe to drop tuning.
