Tom has a review of the 1.33. Check it out and decide if the speed difference is worth it. Overall, the 1.33 is about 7% faster, depending on the application and the game.
Is it worth the cost increase? Again, that is up to you. I don't think it is worth the cost. The difference between the 1.33 and the 1.2 is around $50.00, but to take advantage of it you must go for a DDR motherboard, and DDR RAM, which can now be a $200.00 difference or more.
On the flip side, the 1.33 is more overclockable, so if you are into overclocking, then the 1.33 is a better choice.
However, to me, it is not worth the price. But that is just my opinion.