Titan X - 1080. Considering pricing I was able to get on the X, it was only a few hundred (AUD) for me to upgrade to a 1080.
I have no brand loyalty (I just buy whatever is the fastest single GPU at the time), and as a general rule, Pascal isn't a messiah architecture you would usually associate with a die shrink. But easier to flip the X now and pay a small amount for the upgrade.