G’day Arjan I did almost exactly the same shape change with the sails on my Taipan 5.7 the boat became faster but I regulary pitchpoled until I worked it out a bit. I learn’t in high wind to tie my battens in relatively loosly so the downhaul can flatten the sail not just improve the shape and lay off the top.
On a good reach with plenty of wind I've found in a gust it's much faster and safer to round down with the wind keeping both bows down near the water if you round up you have to go up a fair way to go through the wind way off course which lifts your hull a lot more ready for a knockdown if the gusts solid. If you round down no one can pick you off as your using the full wind strength and you come back up onto the original course as the gust recedes. For me I’ve found boards depend on the course, waves and wind, in big waves I need all of the boards to keep me higher and stop getting swatted off the side by the waves, as in my video on the other thread. Flat water very big wind around the 30 kts I’ve had leeward up windward down so as the gust lifts me right up the boat slides sideways and comes down again but it’s a wet wild ride.