I had the similar goals as you: advanced kite foiler wanting to get into the waves on no wind days and to get up & pump a large high aspect foil on the flat.
If starting a-fresh I would consider a stoke boost ($5.4k aud: half the price of fd gen 2) if id known how damn difficult waterproofing the battery compartment was going to be… seems like a quicker to mount, half price version of foildrive gen 2 with almost as much power/ run time.
I didnt go for the all in one boost kit as the box is 90mm high and the charge port & on switch are on the side so wouldn’t be as neat when fitting inside a board but it does look like a decent option. most boards ~5ft that i liked the look of are around 70mm max thickness and prone board even thinner.
I tried previously the 6374 maytech kit with 100A esc + 8s3p but this wasn’t powerful enough to get me up (85kg) on a big 100l wing board. Ive read the stator is shorter than foildrive (less torquey) and the esc probably less powerfull (~18kg thrust).
it may have been possible with better technique/ paddling, &/or the 130A esc.
other 6374 motors sound plenty powerful enough (but I figured 6579 was only a marginal increase in size/ weight +2mm diameter +~200g.
overall, i’m happy with the 6579 kit, as per notes on my set-up here: 6579 Waterproof Motor with Ceramic bearings - #6 by jbfoiluk