| Well, it is all very simple: the more expensive a guitar is, the better the quality of the wood, and the better the construction. You have to trust the luthier (Alhambra) for that. But the tone or sound and playability is something you have to decide for yourself.
So the only thing for you to do is go to the shop, play them both, and see whether the 8c is worth the extra money. You have to hear the sound yourself, and play it yourself. It is possible that the 5p plays easier for you, or that you do not like the sound, these things are personal.
If possible, take a friend to the shop who plays a few notes as well, or maybe the shopkeeper can play. You can then listen to the guitar from a distance, or even outside the shop, that's easier to hear the difference. You can also take your own guitar for a comparison.
All I say is go there yourself and take your time. I spent 2 days in a shop before I bought mine.
I tell you a little (true) story. My former guitar teacher was looking for a new guitar and he told me he couldn't hear the difference. He borrowed a guitar from the shop to try it out at home. His guitar room was in the attic upstairs, and after playing for some time his wife came up and said: what a nasty instrument you are playing. It was a handmade quitar of over 5000 euro's, 20 years ago.