You really just need to weigh the two along with what your needs are. I had a zd7000 and got rid of it pretty darn quick. I thought I could handle the weight, but it was just too much having to carry it everyday. It was an awesome machine, but heavy, hot, and if you're planning on using PhotoShop, forget about it. There is a known issue with the ZD's chipset and causing the machine to lock, blue screen, and restart while trying to use the program. That said, if HP had offered the same style (full sized keyboard) with the Sanoma chipset and the Pentium-M, I would probably would have given it another try. That would have shed a couble pounds and made it more tolerable from the weight and heat side of things. I remember my wife would complain that our "Bedroom" got too hot when I was using the ZD for extended periods of time. It blew some wicked warm air consistantly out the side. I don't know if the same can be said about the ZD8000. I had the 3.2 GHz P-4 w/HT zd7000 and I'd say my loaded up M680 is faster. Then again, it's faster than my desktop computer running a 3.2GHz P-4 w/HT 256MB Video 1 Gig Ram, multi media center PC too. Additionally, there's a rumor that they will ultimately be releasing the 17" ZD notebook in the near future in a centrino configuration. I gotta kind of beleive it because in it's current configuration it's been out for nearly 1 1/2 years I beleive. The laws of the Universe would point towards it needing a refresh. I myself may take a look at it when they do as I enjoyed it (aside from those flaws).
I run the most intensive apps (accept CAD apps) on my M680 with out any issues at all. You name it I run it; Maya, Dreamweaver, Flash Pr, Adobe Illustrator, Adobe PhotoShop, Ulead PI 10, Ulead Video Studio, All MS Office Apps, and various 3-D games. Often I'm running several at one time. I am to date, still very satisfied.