Changing PhD topic and effect on career I'm a PhD student in my third year (4-6 is common in my country) and seriously consider abandoning my current topic. 
The new topic is in the same general field (CS related), yet in a vastly different domain and would need a quite different methods. My advisor suggested this switch, he could keep me funded in both cases, yet probably better with the new topic.

Arguments for switching are both personal interest in the new topic (it's recently trending, I was interested from the beginning, yet few positions were available) and lack of progress in the current area:


I could produce some publications, yet not up to my advisors expectations (should be easier with the new topic, given the impact factors of the journals my advisor suggested)
For the last 6-8 month I made barely any progress (lots of failed experiments)
I would probably have to abandon my current methods anyway due to 1./2., so half a year or so will be lost learning new methods no matter how I decide


Yet I shy away from switching, mainly due to already being quite old (combination of personal problems and a switch of my major as an undergraduate) and fearing how my C.V. would look if I did take about a year longer and had this second switch...

Thanks for any input.
Most people won't care.

The time to PhD isn't really considered all that important unless it's highly anomalous (much shorter or longer than standard), and if you get good publications out of it, nobody is going to make a big deal about switching topics. It happens for all kinds of reasons—funding changes, or because the original project doesn't pan out for whatever reason (technical or logistical). 

It will also not impact your career much, unless you're planning to continue studying one of those areas as your post-graduation career. Again, the overall quality tends to matter much more than the actual topic in most cases (particularly if you're moving into a different area from your graduate work).