Not sure how exciting a 4.0L with only 425hp would feel from a driving perspective.  Yes, it could have a nice broad torque band which is beneficial in the real world, I just wonder if it will be lacking a sparkling top end rush as you climb to a 8k rpm redline.  This would sort of be like a Corvette motor in Cayman.  Highly effective in moving the car, but a very different experience to the GT3 engine.  

Anyway, 425hp is enough for me in a roadgoing Cayman.  Particularly if it has tighter gearing.