The game not playable, and having pretty big performance issues in recent snapshots

So, I was having pretty serious framerate issues with the 1.8 snapshots, but I didn't mentioned it here, because they are development versions, I tought it's normal to have a bad performance there. But with this new snapshot(14w30a, b, c) it became much-much worse... With the previous minecraft versions, (1.7.x) I was having a nice 60+ fps. With the latest snapshot(14w30c), I have 15-30 fps.
But that's just the smaller part of the problem... Whenever I play, the game appears to be frozen. I can move around, click stuff, but the game is not responding to my actions... Like when playing a multiplayer game, and the server is having issues. I recorded it to a video here:
https://www.youtube.com/watch?v=WP681sUgrX4
I hear a lot of pepole talking about how big performance improvement is the new snapshot, but for me, it turned a game with perfectly fine framerate into a game which is unplayable because of "server-side" freezing and framerate issues. I don't think it's an issue with my computer, since I can switch back anytime to 1.7.x, and it's working fine.
I didn't mark older 1.8 snapshots as affected versions, because they only had bad framerate, not these freezing issues. I've triggered a debug crash too, just in case... it's attached below. Tried with a freshly re-installed windows as well.
Thanks for your help, and sorry for my bad english.
Edit: Screenshot of my CPU, memory, GPU and disk usage: http://i.imgur.com/oieneQN.png