There are many boats that can cross oceans.
I know that my boat can cross oceans. If I don't end up crossing one then it'll be all about me and not the boat.
I think the "me" part in some minds implies skill and while that is important, there is also the "me" part in comfort. There are many boats that I know I could cross an ocean in, but I would not. I look back to the Nordhavn Atlantic Rally in 2004. Many of those aboard had a miserable time. There was a tremendous difference in the boats and a lot of it was size.
If I could have crossed on any of the boats involved, it would have been the 90' Monk McQueen. I would have been ok on the Nordhavn 62's and 57's and the Seaton 55. However, based on that rally, there is no way I'd cross on the smaller Nordhavn's. There was a 40', five 46's, and one 47'. They all made it but some with a lot of assistance. A lot of their passengers did not enjoy it. Now, I think part of that was expectations as I don't think many were at all mentally prepared for the conditions.
For some, just making it across is enough. I've followed the stories of many who have crossed. Richard has crossed both ways in a KK 42, but that doesn't mean I'd choose to do so in the same boat. It has nothing to do with whether I could or not. There are many things in life I'm probably capable of, but don't choose to do.
I'm not sure where my cut off is. I intend to cross in larger when I cross but I'd be ok in many in the 60'-80' range. Unlike Ted, I don't insist on steel, nor do I need 6000 nm range. I'm fine with 3000 nm range at intended speed and knowing I can slow and increase it to 4000 nm or more. I'm less comfortable with a 2000 nm range at 8 knots, knowing I must slow to 6 knots to have 3000 nm range.
Some crossing single handed and some cross with a crew of two. I'd never cross with less than four and at least one would have far greater technical and mechanical knowledge and skill than I do. I have no concern with my skills at the helm, but I'm not adequate in the mechanical area for such an endeavor. I do believe though in being able to get adequate sleep and in just having enough time to relax and enjoy.
Part of it comes back to the question of why cross an ocean. For some it's a competitive type thing, to challenge themselves. For me, it's for the pleasure of seeing things from a different perspective, of seeing the beauty of the ocean and experiencing being days from land. It is something I do want to experience at least once in my life, but I want to experience it with some degree of comfort and safety. I also want to experience it with others, not in total solitude, to share it with my wife and family/friends. Some want to do it to prove they can. I never feel the need to prove anything to myself or others, I simply want the experience. I'm competitive on a tennis court, on a basketball court, or at a card table, but not on the water.
As to your 54' KK, I don't know it well enough to know if I'd cross in one, but knowing what I do know, I'd consider it. There is no sub 50' boat, I'd consider it on.