at 54kg a 7.5m is huge.
a 80kg person will benefit/plane quicker from changing from a 7.5m to a bigger size say a 9m or 10m.
for you the benefit will be much less.
if you want to plane earlier, rig your 7.5m sail fuller.
buy a carbon fibre ultra light board!
i use a fanatic 75 wide by 275 long, this board with my 7.7m is big enough for my 67kg.
including straps it weighs only 8.5kg.
found using sails of 9m plus to be tiring and not very enjoyable.
if you do buy larger sail, a sail with less battens/cams is easier to use.