A bit of an update after a lot more sailing of the board.
After a big session on the lake yesterday (Ben & I did over 130km ea), mainly on a formula board (with a Reflex2 9.7 - gusts up to 24 knots), I switched over to the Phantom (with a 9.2 Reflex2 sail) and I reckon I had more fun on the Phantom! Don't get me wrong, the formula was great fun, and generally faster on all points of sailing, but in comparison to the Phantom the ride on the formula can be quite harsh, bashing into chop or tramping over it. The Phantom just slices through the chop upwind when railed up and off the wind the the sheer size of the board seems to smooth out the jolts.
The best run of the day was the last run, from the South end of the lake to the North end on one broad reach - about 6km well powered up

. The Phantom is so comfortable and well mannered - it was a hoot. Ben was on the AHD and this was just as quick.
Things to note : 1) if well powered up, rail the board so that the footstraps are dragging in the water - the angle upwind is a little better and acceleration in gusts is a little better. In lighter winds don't rail the board so much - the drag to upwind angle ratio seem to increase when not fully powered if tilted too much.
2) with the mastrack fully back, and in the back straps the board will not "tail sink" even if only moving slowly. This means that this position can be employed a lot earlier than most other raceboards. It also makes pumping to stay planing easy - you don't have to scamper up the board and slide the mast track forward to stop the tail sinking.
3) the footstraps supplied with the board are a bit soft for my liking. They tend to collapse or twist the "wrong way" sometimes making it hard to get the foot in quickly. I've replace the back straps with ones off my old formula board, and stiffened up the beating straps with plastic strip.
The 9.5 raceboard sail (mine is a Severne) is well suited to the board, providing good power to help railing, and certainly improves tacking. The board also pumps very well with the raceboard sail, particularly downwind.
The weak point of the board may be in the 5 knots of wind range - this is probably also related to my lightwind technique. Older, traditional raceboards are probably marginally faster in these conditions, maybe related to the Phantoms wide, flat surface area underside. Hopefully all the races in the upcoming Oceanics at Hawks Nest are in windier conditions than this