Great thread, keep it up. A few comments:

Flat bottoms are much easier to build and repair.  After fairing, fitting and installing floor bulkheads is the most soul destroying boat building job.    They also allow lower headroom, if the hulls are designed right.  The weight and windage advantages of these outweighs any small difference in wetted surface/friction drag.  

2 (or three) piece sleeved masts for trailering are no problem, and not much harder to build than one piece (the joining sleeve is a cut off piece of one section slit and glued into the adjacent one.  The important part of the build is that everything is straight, which is as easy/difficult for short bits as long.  

My telescoping round mast was probably more work than it was worth (I don't go under bridges or have to tow my boat, which changes the pros and cons), but telescoping wings have some potential.  A couple of weeks ago a client was here and we played with attaching sails to masts with hoops, which make telescoping rigs more viable.  The results were promising, he will use them on his 18m/60' mono.   More exciting is the work Steinar (he is visiting, the ideas are flowing thick and fast) and I have been doing on a telescoping wing mast (60% of the chord) for his boat.  Ordered the sail yesterday for a short length of 1/4 scale model.  If it works, it has low sheet loads, little or no twist (ie no vertical sheet loads) and no boom.   Results and pics next week, maybe.  

Reefed sails rarely set as well as unreefed (the sail luff is cut for different mast bend characteristics ) and the drag of the top mast is slow.  As Mike says, a bigger issue on a stayed mast than an unstayed one.     

A 30' cat will weigh near enough the same as a 40' proa for the same accommodation. The 18m/60' of cat hulls are shorter than the 20m/70' of proa hulls, but the proa hulls are lower and narrower.  Therefore the sail area can be the same, although the proa will have much more righting moment.  The proa accommodation will be more usable.     The proa will be quicker to build (easier hull shapes, only 2 appendages, no unnecessary curves, one simple mould usable for both hulls/decks), faster, safer and more comfortable as it is longer and both sails can be seen without having to turn around.  It will also cost more in a marina, but it will have a tender big enough that you can anchor off, motor in and avoid paying altogether.     

New Ex 40 drawings are finished, will be on the web page when Steinar stops doodling telescoping wings.  ;-).   First one is being built in Barcelona.  

We have also designed the latest "best ever" rudder mount after 2 weeks of discussion, sketches and finger drawings on the beach.   Simpler, lighter and easily mounted on the inside or the outside of the hull.  First part of the laminate for an El test version is curing as I type.    It works for bidirectional or one way rudder sections (NACA0012).  

We spent today working on rudder build methods.  I drew every one I had tried or heard of in the sand (about 30m of sketches) and we picked them apart.  Came up with something simple and quick. 

Had a sail on Kitetik (15m Solitarry, weighs about 500 kgs/1,100 lbs, plus 3 crew) yesterday.  25 sqm/260 sq' (20 sq m projected, which is less than a Tornado cat) leading edge inflatable kite, dirty bottom, 10-15 knots of breeze, 30C air temp, a beautiful day.  Top speed 8 knots, pretty poor up wind.  For the first time, all the systems worked, so we can now move on to boat improvements and bigger kites, starting with a converted 28 sq m (28 sq m projected) paraglider. .