I would shy away from the GTR based on the fact that it is a 2009. If it were a 2010 or 2011 with the updated transmission coding / work it may be a different story.
Additionally, as an only car IMO the 1M is better.
I will say this, i would NOT pay 60k for a 1M. As others have said, too many good cars hover around that price range. For example, the excellent 997tt is around 60-70k used.
I love my 1M, and wouldnt trade it for anything in this price range.
I just tracked the car, and with a stage 1+ tune, the car has plenty if not too much power for the track for an average driver. It was really fun