How does it look if I finish my PhD in five years instead of four? I’m doing my PhD in computer science in Germany and next year would be my 4th (last) year. I can wrap it up until then, but I really like to have an extension to the 5th year. There are still 2–3 ideas that I have investigated but couldn’t finish because of the time frame, so I would like to do a bit more. 

I have two publications so far and hopefully can have one more during the coming year, but I would like to have more publications, especially in better conferences. Also I think that I do not have yet enough expertise on the topic I’m working on.

Anyway, my supervisor prefers that I finish my PhD in four years, although I haven’t talked to him seriously about it yet. Also the funding would be available outside of his grant budget so he won’t be worried about it.  

I’ve heard of many other students who finished in five or even six years, but I’m not sure in practice how important it could be especially if I can have good publications by extending my PhD.
The quality of your thesis overshadows the length/duration of your PhD. 

Having said that, it depends on your goals. If you clearly think (and your adviser as well) that another year would make a big impact on the quality of your thesis and, consequently, on your CV, and is not too risky to pursue extra work (i.e., the questions you want to tackle are not too ambitious and you have a good possibility of enhancing your CV) then go for it. Otherwise, I am not sure you would want to stay at PhD while you could be looking for your next (PostDoc or industry) jobs.