I would have to ask what experience you and your girlfriend have in terms of sailing. The Pacific coast can be rather challenging, especially if you are leaving that late in the year.
I would also ask what boats you've had experience sailing on? Do you really have any idea of what you are looking for in a boat??? Do you know if you or your girlfriend will get seasick or not, and under what conditions???
I'd point out that a boat that you'd need/want for rounding Cape Horn is not necessarily the same boat you'd want to do a Panama Canal crossing.
IMHO, you really should get the boat at least six months before you plan on departing. This is so that you can sail the boat and get used to her and figure out what additional equipment and modifications you'll want to make to the boat before you leave on your voyage. This is also so you can gain experience sailing your boat on progressively more difficult and longer voyages gradually and shake down the boat so that you know what works, and what needs to be modified.
I would point out that you may be better off looking at boats on the smaller size of your boat range, rather than larger. If you've not read Beth Leonard's The Voyager's Handbook, 2nd edition, she has a good section on why starting with a smaller boat is a good idea. Among the reasons getting a smaller boat is a good idea are:
For each additional 10' in LOA, the maintenance chores double and the boat-related costs triple.
Larger boats have more rigging, more systems, more deck area, more hull, larger and often more complex deck gear, larger sails, etc. Many places charge mooring and slip fees per foot, as well as costs for haulouts, storage, etc.
In many places, a large boat will limit the choice of marinas and make it harder to get fuel and water
It will also limit the moorings and slips the boat can use, as well as the number of hurricane holes you can use. Larger boats are also less likely to be used for daysails and such... if you look at any marina, you'll see that the use of many boats is inversely proportional to their size.
Larger boats are also more likely to attract thieves and pirates, since smaller boats are usually considered less valuable as targets.
Though Hawk (47' LOA) is much more stable than Silk (37' LOA) and therefore much "safer" in extreme conditions, Silk was much more forgiving. If we misjudged a squall and didn't get the chute off in time, we could wrestle the sock down over it and manhandle it to the deck. If we wrapped the jib during a jibe, we could unwrap it by hand in light air and with a winch in windy conditions. But brute force gets us nowhere aboard Hawk. She requires much greater forethought, because the forces she generates quickly become unmanageable and dangerous. Silk offered the perfect learning environment while we made every mistake in the book; Hawk demands all the skills we've acquired to sail safely and efficiently.
Smaller boats are often far more forgiving. You can often push a smaller boat away from a dock or haul it into a dock with a spring line, unaided, but try doing that with a larger boat, and you're risking life and limb.
Before we started sailing Hawk, I'd been of the "bigger boat, bigger winches, no problems" school.
Yes, larger winches, an electric windlass, etc., can make sailing a larger boat easier, but that doesn't necessarily mean the boat will be easier to handle. Carrying the sails or anchor and rode out of the locker requires more sheer strength than doing so on a smaller boat. What happens when the nice powered accessories you're relying on fail??? Hauling in the anchor rode on a 45' boat is often much harder than doing so on a 35' boat, as are carrying the sails, flaking the sails, coiling the docklines, etc.
Just some food for thought.