I'm getting terrible performance with 1.8 on my machine, as if there are too many things to render. Even on a brand new world, my computer struggles with the framerate with nothing but land and trees, so I'm not quite sure what's up.
I have a few things to try such as downgrading to a smaller texture size, which thankfully the texturepack I like has a lot of, so I can have the same one at 64x If I wanted to, but it does seem like the game is getting increasingly demanding. It must be a combination of the new lighting system and the increased polygon count on the animals. I also did notice, that at least on the texture pack I'm using, that mob textures aren't limited by the shape of the mob anymore, for instance the sheep has hair that goes beyond the regular sheep shape, making it appear longer. The game also seems to be crashing even more quickly now too, every 5 or so minutes instead of 15 minutes making it almost impossible to do anything, so we'll see.
So, yeah, I'm going to try a few things, such as trying it on my Mac, but I'm expecting that to be a little awkward since all I can use is the trackpad on it.