twin handed dinghy

420 is a good shout! They're not slow and are a good place to learn the art of trapezing.  For a trapeze boat you really should have the bigger one of you crewing, and remember hiking boats can be just as fun!  I have always found 29er helming to be a bit dull... obviously its not easy, but the crew does the majority of the physical stuff upwind.  It gives you a good start in skiff helming for sure, but trapeze helming such as in a 49er is a whole lot more challenging.

29ers are particularly good because you learn to trust each other very fast, and if you dont then you get wet!  you will quickly learn a fine ballance between the crew playing the mainsheet and steering to the wind, it is very interesting how you eventually manage to effectively read each others minds when responding to a gust etc....

Then there are boats like the 420 which is more balanced between the helm and crew.  Definitely not a boat to be excluded because it doesnt look skiffy. They are certinely not slow.

4000 is a good boat, but probably too heavy and they again arent class leading in my mind...

500 sounds like a good boat for you but you are probably looking at about £4000 at the least for a second hand boat, but it would be in good condition because they are so new!!

Just don't rule out hiking, probably the best fleet at the moment for you is the RS200, such a strong fleet and loads of them! and you can pick one up cheap!

There are too many to choose from!

The 420 isnt really that heavy,

Although with 130kgs in the light stuff (sub 10knts) you will suffer, saying that quite a lot of the teams i know sail with around 125kgs and they get on just fine! we sail with 125kgs and it does take a fair bit to get it going.However, once it starts to get breezy its a great boat! The upside of one compared to the 29er is that you can happily take one out in over 20knts without any problems, especially with your crew weight. One thing i would suggest if you were to go for one would be to go to some class training. They teach you loads about rig set up which makes a massive difference in these boats!