For mere mortals there is very seldom any reason to have more battens than 5, or even cambers, on sails in the 5.3 range. Control is perfectly sufficient, for most users.
On the other hand, you might compare it to a speed and high end oriented sail, like a slalom/race sail with 3 cambers. Then it may well be that a 6.5 Race sail takes a lot more wind than a 5.3 wave type sail (they could well be overlapping). You seem to already have a 6m2 Slalom sail from HSM, how race-oriented is that one?
A 5.3 wave sail for a 54 kg windsurfer does not sound like a highwind sail. It is something that should take you planing already in about 7-8 m/s.
What is high wind for you? If it is more than 10-12 m/s then a wave sail does not have to be any bigger than 4.5 m2, probably smaller...
Check out "http://videojibe.com/featured/windsurfing-sail-size-calculator/" to learn how different sail sizes fit different weight windsurfers. I think the calculator works well for "Freeride" type sails. Disclaimer: I am not sure how reliably it works with really light sailors like yourself.