Boomless main sails... It is kind of a trade of - ease of use for performance. For not having to watch how one of your daughters gets smacked in the head you will loose some trim options / outhaul. I think that cats with their wide rear mounted traveler systems can handle boomless sails quiet ok. A loose footed main with some lightweight boom like setup for outhaul control and trim is a nice compromise.

The 25 to 30 m days... There will be few. During the few I get I am not at all worried about the performance of my outdated Hobie. I am mostly worried about staying upright and getting my next tack sorted out. I would not recommend to take your kids (especially considering their training level) sailing on those days. This is more one of those days where you call one of your sailing buddies.

FX one... that would be a bad choice for you (family and so) Actually since I am thinking about it, buy one, get real frustrated with it and sell it to me next spring for cheap!

Nacra 570 ... I think this is much more family friendly. I would keep this one in mind if you have the $$$ for it.

One other thing to consider is what it takes to righten a cat after a capsize. The 16 foot boats can typically be righten by one adult and the proper technique. This might not be possible for most of the 18 foot cats.

Patrick