The reason it's not exactly worth it is that even the highest-end laptop parts are about equivalent to mid-range desktop parts. For example, the 6990M (ATI's fastest available mobile graphics) is about equal to a desktop Radeon HD 6870.
If you choose between the 2760 and the 2860, the difference between the two is 2MB L3 Cache (not very important) and 100 MHz at base speeds (not Turbo, which is equivalent). I'd choose the 2760 over the 2860 and save some money, there is no real noticeable difference between the two. Again, note that this will only perform like a mid-range desktop; the 3.5 GHz Turbo is not meant to be sustained, and the laptop thermals won't allow a sustained burst of speed anyway. It will mostly perform like a 2.4 GHz quad-core.
Another reason it isn't really worth it is that you can't effectively upgrade anything outside of RAM and hard drive capacity, which means in a few years (you have a nice build, I'd give it 5 years of competitive relevance) your $3000 laptop will be outdated.
All that being said (sorry to sound so negative
), I'd go the 2760 if you're not willing to jump to the 2960. Best of luck