I can't comment because I don't have a FW myself and I've not ridden yet the Phantom in the upper wind range at full planing speed.
When doing drag racing between a slalom and a 2010 Phantom 380 Race carbon, however, I'm always faster on my HS105 than my pal on his Phantom + 9.5/7.8 m2 sail combo when we are fully lit (I'm overpowered at about 12 knots constant wind with my 11 m2 sail or at about 15/16 knots with my 8.2 sail). Keep in mind that I'm 10 kg lighter than my pal, that I always ride larger sails than most anybody else on my home spot and that I have a 10 years training experience with my board and sail quiver combo while my pal has only a 2 years training experience with his board + sail quiver combo. Also keep in mind that the Phantom 380 is a true raceboard, so it does take quite a lot of TOW to train and to acquire higher and highers skills with such a board, especially in the upper wind range. So, my home spot comparison should be taken with a large grain of salt to be fair and honest and may be Rémi can beat me with his superior raceboard skills.
I'll leave that to other experienced Phantom 380 + FW riders to tell us what their experience has been so far.