The CPU is dual-core. The iPad 2 CPU was also dual core. It might be a bit faster or it might be exactly the same, we won't know for a while yet, but don't expect much improvement.
The GPU is quad-core, where the iPad 2 was dual core. 2x faster. But the screen has 4x more pixels to draw, so on paper it's only half the speed of the iPad 2. In practice games don't need 4x more power to draw 4x more screen though, so in practice it'll probably be similar.
I reckon you won't see much speed difference, basically. Just a big quality improvement.