Footage from yesterday (2nd session on the 6.4) wind strength was perfect for this size wing at my 90kg weight.
Afternoon started 8-13 so I used the infinity 99 wing with 42 rear (position B, long fuse, 90cm mast) the foil whipped up pretty good with some pumping. The 6.4 settles down really well, feels solid in your hands.
The biggest difference I find between the 5.4 and the 6.4 is, the back hand on the 6.4 I use the first back handle, on the 5.4 I use the 2nd back handle. If the wind is super light moving to the 2nd back handle on the 6.4 and pumping it hard it gives you some stump pulling power, its incredible lift.
The wind filled in pretty sweet with average wind speed around 13-16 so I switched out to the infinity 84 wing and kept position B etc, that was plenty of power and made gybing much easier. The 5.4 is easier to pump and does feel lighter and of course the 6.4 is bigger, more powerful so naturally it pulls you up on the foil with less effort.
3.5 hours later I was getting cramp and was whooped, very happy with the performance of this wing and it ticks all the boxes.
for my weight 90kg/200lbs on a floaty board, fresh water, gusty winds with either i99 or i84 foil:
6.4 for 8-15 knots
5.4 for 12-20 knots