In my reading, if it's not worked in 24 or 48 weeks, an extra week isn't
likely to make a different.

Given that 24 or 48 weeks is like a dart thrown by a semi-drunk man at a
bulls eye target because he's done it three times before and it hit the
board, I think that any benefit is more likely to be psychological.

I stopped a week early on on my treatment and got an SVR but I was an
unusual case.  If you're spending time thinking about it, just do it.  

I have to agree with Elmo.  I don't know whether 1 week is going to
make a difference but I do understand you wanting to give this your
best shot.  I also considered extending my treatment because of fear
of relapsing.  Good luck.