Love my C400 MKII
I bought a C400 MKII in 2001 that was less than a year old and had already been commissioned. In the 5 years since, I've had this boat in a variety of conditions. I have the roller furling mainsail which probably hurts me a little in light air but the 155 makes up for it. On the other hand, most of my sailing is in relatively heavy air with 20kts on an average day and the boat handles very well I think. I think the biggest problem I have in handling the boat is a bit more weather helm than I would like. Having said that, I use the mainsail roller furling to balance the boat and it works pretty well. I've had the boat in 45kts and breaking seas (single-handed) and never felt like the boat was out of control; in the same blow, I hove to in order to get some rest and with the sails properly balanced the boat sat very well and comfortable. I singlehand this boat a lot and I think it's pretty easy to sail by myself. I find the dual helm useful--when sailing I can stay on the windward side and have great visibility; it also makes docking alone a little easier (now if I could just put another throttle lever on the other side...).
Most people comment on the roominess and "dockside" comfort of this type of boat and that is certainly true with the C400. However, I think it needs more dedicated storage and lockers or at least better organized lockers (the cockpit lockers are large and deep but feel like a huge hole that everything wants to fall into). The worst thing about the interior is that the cockpit sole is pretty low over the aft bunk and it takes a little while to get used to it (ouch). The companionway is a little on the steep side but enables a nice bridgedeck--keeping water outside.
Overall, I truly enjoy this boat and find it a really good compromise between comfort/liveability and sailing capability, especially it's easy of singlehanding considering it's size.