Which is more impressive -- finishing a PhD in 2.5 years or getting more research done? I am working on a PhD in chemical engineering, and my advisor mentioned to me today that I'm on track to finish in about half a year.  I only have one class left to fulfill the course requirements and I have a few papers published, with a couple more almost finished.

Personally, I'm in no hurry.  I love grad school and working on research.  However, from the perspective of a getting a good job, would a PhD at 23-24 years of age or additional research publications in high quality journals look better?  Once I graduate I plan on either doing research in industry or working at a startup.  I don't plan on going into academia.
In my field (computer science, broadly), my impression is as follows.  It is of course an over-generalization.  


If you want to go into academia or industrial research, then what you
do during your Ph.D. matters much much more than how long you took,
though if you take more than 6 years to finish it starts to look bad.
On the other hand, if you want to go into non-academic industry, you
might impress people with a fast Ph.D. because you'd show yourself to be the sort of person who can finish big things fast.


If you're only 2.5 years in, unless you have an offer from someplace and need to finish ASAP, and especially if you're enjoying your Ph.D., I wouldn't rush to graduate that quickly.