I just read this, http://www.macworld.com/article/132330/2008/03/macbookpro_bench.html
"The new 15-inch 2.5GHz MacBook Pro was quite a bit faster across the board than that build-to-order 2.6GHz system—more than 8 percent faster, in fact, in Speedmark, and 23 percent faster in Photoshop. Doubling the video memory also helped the new 2.5GHz MacBook Pro best the older build-to-order machine in our Unreal Tournament test by a whopping 34 percent."
Not a HUGE devastating one but a fairly noticable gain I'd say.
"The new 15-inch 2.5GHz MacBook Pro was quite a bit faster across the board than that build-to-order 2.6GHz system—more than 8 percent faster, in fact, in Speedmark, and 23 percent faster in Photoshop. Doubling the video memory also helped the new 2.5GHz MacBook Pro best the older build-to-order machine in our Unreal Tournament test by a whopping 34 percent."
Not a HUGE devastating one but a fairly noticable gain I'd say.