I ask this in all seriousness: Do you think you can really tell the difference between an 8 and a 10?
Having been there on a 10 day, I don't think you can. The parks are huge. It's the queues times that change.
I was at Epcot on a 9 day AND it was New Year's Eve so people were trying to crowd together... the fireworks, dance parties left and right, overflow from bars and restaurants, people wanting to chat and celebrate, etc. We walked on to Space Ship Earth, no wait at about an hour before midnight. Twice. And we still made it out for the fireworks and more dancing. We did miss most of the Silent Dance Party. Almost a fair trade, I guess.
I watched a couple of videos about parks on 10 days and I can't help but notice that the really manic ones are filmed right next to lines or right after parades. Plus the camera compresses your line of sight, so it looks like a sea of people. For brief moments, it really does look like that and 10 minutes later, it goes down to something reasonable.
What can really get you is rides with not so obvious lines. On Dec 28th, the Muppetvision show looked like a 20 minute wait for a 20 minute show. That's what the sign indicated. It was more like 45 and we ended up back behind the theater for a good bit. It was all dark and cold back there. If it hadn't been so funny, I would have lost my mind. I got in line because I like Beaker that much. Realistically, the sign was totally accurate, 20 minute wait for a 20 minute show plus 5 minutes to clear people out a couple of times. It's the arrangement that is deceptive. On a crowded day, 45 minutes is nothing. That was my worst experience which really isn't that bad at all.
Animal Kingdom is a massive area with only a handful of rides. That should totally be manageable with a couple of FP's. The only problem with AK is the few rides they have are worth doing twice. You'd have to be a real die hard to do that on a busy day. I suspect you could do with a lot of patience.
The flip side of AK is, it is really beautiful. I'd burn a ticket and a day to walk around the park.