7x4 or 7x5. But in truth the Enya is not a very powerful engine. I used one with an old Topflite white nylon 8x4 and it worked well but those old props had a reputation for running flatter in pitch than the numbers said.

Pusher props are always a pain to get. But check the APC and Master websites for what they have.

Given the weight of the Aerofly and the fact that it doesn't use a high tech airfoil to let you at least take advantage of the speed that would normally come from such a heavy wing loading I can't help but think that you would be best off to move on to another model.

Or at least modify the Aerofly to a nose mounted engine so you can loose a heap of the nose ballast. Things may perk up enough to let you get some decent air time that way.