I concure with Carl. Having owned all on his short list and sailed all of them with combined crew weight in the 330-370 range. Hey! I'm 200 lbs of it!
My first choice would be the Nacra 6.0 -- it carries the weight well but, can get over powered quick for an inexperienced crew.
My second would be the Hobie M20 -- for a few reasons. First you can race it anywhere in the US. Generally, they are built very well - post 1995. and are fairly user friendly. ALthough if you race, everyone else will kill you due to the CWM is 295 (still - I think, its been a few years since I raced that one)
Buy one used! You'll have more fun and usually it will have all the bugs worked out.
Thanks
Steve