This doesn't seem to work anymore, getting a CTD every time I try and travel between them.
Tried changing everything, nothing works.
The weird thing is I can travel from anywhere in the Tamriel worldspace to my new worldspace just fine, so I know the world isn't the problem.

Help appreciated, this is driving me nuts. Also seems to be a recent thing, I'm just going back and testing things and now it's started to happen. Used to be fine.

Bumping, searched everywhere but I see this question asked a lot with no real answer. Is it just not possible?

You have to do it by teleporting to a clear memory buffer cell first.
I had the same problem. It was OK at first, then as my mod grew in size,...BANG CTD all the time.
It turns out that small mods will teleport you back OK. As the mod grows in size, more memory is used ingame. This has to be flushed before you can teleport back to any worldspace (apart from Tamriel for some reason).

Read this link -
http://www.gamesas.com/topic/1362739-grey-screen-on-coc-to-towns/

It sounds like you have the same problem

strangely, when converting the file to esm, the buffer isnt necessary. all ctd's are gone. (navmesh bug related?)