Generally more pixel pipelines is better. But with some of the newer radeon cards it's a little different. Which cards are you looking at? What's your price range for a card?
Usually pixel pipelines make quite a noticeable difference in performance. That's not to say that one card with 16 will ub3r pwn one with only 12, but in most cases it will .
I would say that this is probably your best option in that range http://www.newegg.com/Product/Produ...19+1068409614&Submit=ENE&Nty=1&Subcategory=48
it's essentially the same card you had picked out, but with a factory overclock. The only real competitor would be the one x1950 pro that's in that range. Im not exactly sure how the 1950 pro and the 7900 gs match up though.