Biggest updating speed difference I found is not adding large files directly into Xara. PDFs, MP3s, MP4,s etc. I add these using FZ then link/placeholder them in Xara. That way Xara isn't checking/replacing large files every tweak.

Never used Magix M or Xara's hosting, but unlike Acorn, I've not noticed a difference in uploading via FZ or Xara. I also don't have huge sites, so it may be that.