Which is more impressive -- finishing a PhD in 2.5 years or getting more research done?
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.