In answer to your question the 88" Extra is a superb machine, it is the smoothest 50cc plane I have flown, in terms of precision it is brilliant, very precise, but turn the rates up and it is a 3D machine, hovering is sooo easy, I had it on the deck on its maiden and it just sat there, also I had a dead stick on my second flight as I had just retuned the engine, but it certainly is a floater, no problems at all, I think mine has come out at around 16.5lbs which is very light for a 50CC model so the DA50 proves to provide supeb power with the ES pipe.
I don''t really want to compare the two planes out right as that would not be a fair judgement, obviously they fly differently due to the size, weight etc etc, but if you are looking to get a 50cc machine, the EF extra is certainly the way to go!

Build thread, pics and video here: http://www.rcmf.co.uk/4um/index.php/topic,46011.0.html

As for the 78" extra I have not heard anything, the next plane to come from EF will be the electric yak, the replacement for the old 55sp-e taking the same setup as the vanquish this time though.

hope this helps
regards