Mathematica 7 vs. 6: A Comparison of Computation and Image Processing Features

[Newspeak]

I use Mathematica for computations and simulations-- and making pretty pictures. So is it worth it to purchase Mathematica 7.0? Or should I stick with 6.0? From what I have seen and heard, Mathematica 7 incorporates a lot of image processing features that are pretty neat. How about computation and simulations? Are there any noticeable differences between 6 and 7?--new features?
Any input appreciated.

 

[DavidSnider]

I don't know how well Mathematica 6 supported multicore processors. From what I hear some computations\simulations can go like 50x faster with the new multicore support.

 

[shoehorn]

I use Mathematica for computations and simulations

Is there any other way to use it?