I took the main points from this thread and I will try my best to provide a complete answer to your Q. My method is that a complete answer has 3 parts – What is the current state, what is the future (desired) state what is the method to get there. (Roadmap to connect current and future.) BTW, obviously the more details available on current and future state the better the roadmap and the successful result!

Current State:
1. You defined yourself as a novice without sailing and cruising experience.
2. You did not give any additional information about you which could be related and potentially assist in your adventure. (Age, physical ability, experience on the water, solitary sports, engineering or mechanical experience, economic situation, etc.)
3. You seek specific advice on the “right boat for the job of rounding cape horn and long term sailing” =>Translation: You want a boat that is extremely tough and capable of going to the most difficult places sailors might go and yet is large and comfortable enough for full time long term sailing.
4. You currently have no time to invest in crewing and learning with other trips on other boats. I do not know if you have time to prep and customize a boat once you get her however I’ll assume you have the means to “buy the lack of time with a lot of money”
5. Your target boat is 36 – 42 (not sure how you got that range as a novice however it is in your “specs”)
6. Side note: You did not indicate crew availability, capability and size so this “small item” will have to be added to the equation. (it has a major impact on boat size, systems, etc)

Future state:
You want a boat that will allow you to sail from North America south and round Cape Horn safely. A boat that is suited for long term full time live aboard. You do not want any other advice about knowledge, learning, experience, Etc. your clear net request is “just give me my target boat.”

Roadmap:
Get yourself a solid steel boat that is professionally built from a solid designer. The size is dependent on crew size however I would be in the range of 40 to 50 feet where the 40 is for a single sailor only and the 50 is for a full crew of 6 (which is my preference for such a trip) For the above I will provide you with an example of my Roberts 53G so you can go to my web site an see how she was designed and outfitted for a no limits global cruising: www.Aliza.TalkSpot.com

Additional note: There is no problem with lack of time, knowledge or experience if one truly internalizes the relationship between these three and the safety factor of the overall adventure. I think that members of this forum mad an attempt to educate you about that relationship. I am a 30+ years veteran consultant in high tech IT and know that the client is always right and needs to get his answers in the most professional way. The above is mine given the information I got from the board.

If you want a more complete answer you will have to go to my “Sail n’ Cruise Dream Fulfillment” web site (based on my “other career” of building SY Aliza, a successful circumnavigation, and additional blue water sailing and cruising for 20 years.) Check it out and see if there is a way I can assist. www.SailnCruise.com

Fair winds and good luck!
Efraim,
"Luck favors the prepared mind" Louis Pasture