We own a Catalina 400 MKII. Love the boat. I single hand a lot with no problem. It has in-mast furling which makes it easy to run. Below 20 knots of wind, it is really easy to handle, and sails very well. Over 25 knots it wants to be reefed. Depending on the sea state and heading, I might reef the main, the jib, or both. With the boat de-powered, it stands up nicely, and handles swell and waves very well. Here in Santa Cruz (just south of San Francisco) I often sail in open ocean coastal conditions. The boat is very well suited for this. I have seen reports by owners who have taken their 400's across oceans successfully. Like any other crossing, preparation is the key.
There are a number of ways that these boats have been modified. See the Catalina 400 Yahoo Users Group, or the Catalina 400 International Association for examples. On my boat I've added grab rails for the two wheel binnacles, and a isolated cockpit VHS. I've got a bow thruster which is convenient, but not a deal breaker. Like I said, lots of possibilities.
We love the aft cabin, but recognize that the limited head-room while in bed is not comfortable for everyone. The interior is beautiful, with lots of hand-holds, although I would add several handholds to the galley if I were taking it offshore. Tankage and storage can be a challenge, but again can be handled to meet your needs.
I love the space, which is perfect for our week long cruises, but most of all I love the way it sails. Our boat moves with power and grace, tacks with ease, and balances so that it tracks along without the autopilot. Feel free to PM me if you want to make phone contact.
Scotty