General note about 3 vs 4m
Get both - they are cheap, they are small - and there are no redundant sizes in peak line like with other kites - steps are just perfect between them.
Peaks have very big absolute range but optimal trim range is quite small - rig big and even depowered peak fluttering will pull you downwind /there big is difference to be kiteless and have 10kg downwind pull on HF/
On 20knts Peak 4 is just too big. And smaller Peaks are everything Peaks are just MORE
My experience about turning speed power to power vs wave Leis they turn faster. Trust me you dont want them turn any faster. /Still im talking about 5,4,3 - bigger sizes are for some reason disproportionaly different - for the worse
And also do yourself a favor and DIY light carbon bar for them - the lighter kite is the more you will appreciate light bar.