The question, while old, is still up to date. I wanted to share for those who come across this thread that the vim answer is not fully satisfactory as I read in the vim docs : "The encryption algorithm used by Vim is weak" which is not the case of GPG.

I fear for now I will stick with GPG asymmetric encryption and emacs. The drawback is that I need to backup not only the encrypted file but also the passphrase-protected secret key.

It's one more risk to lose my data. I feel we always have to choose between a risk of data theft and a risk of data loss.