Beginner foiler here (kiter since august 2018, foiler since april 2019), so I probably need quite a bigger kite than someone technically better and more refined.
Largest size for me is 17m Airush Ultra v.2, on a Moses Onda 633 foil.
I was very skeptical of getting such a large kite, as everybody seems to agree "smaller is better" and "too large means too quickly overpowered", but at probably 115kg dressed with wetsuit/impact/helmet/harness (and even more when wet), I really need a serious kick to get on the board and get the mast out of the water in *low* winds.
The 17m will get me up in 7 knots (if I'm lucky even a tad less), which is huge for me: it basically means I can kite every single day or so if so I wish.
A much better kiter/foiler in my spot, with a similarly large hydrofoil but only 83kg of weight was able to get up and foiling below 6 knots on my 17m.
Downside of such large lightweight kites is not much being overpowered (which happens quickly, but in stable conditions is very manageable...), rather, it opens the doors to really kiting light winds, an opportunity that comes with the liability that, if kite is dropped (by mistake or because of a lull), it will never relaunch again...