A couple of items quickly come to mind:

- Pop up rudders (~center boards too~)
- roller furling jib
- overall length...i.e. a 20' cat is more stable in short steep waves than a 16' cat.

You're going to get a lot of 'my baot is better than your boat' before long but the Nacra 6.0 has a reputation of being a very solid beach boat. The Hobie 16 does too largely because it doesn't have centerboards to deal with when beaching. It's a bit small for my tastes though.