A bunch of information about the ARM Cortex-A72 processor core was revealed at yesterday's ARM TechDay 2015 event in London. At the conference, ARM explained the decision to use A7x naming is purely marketing driven, it's an attempt to give better differentiation between its high-end and mid/low-tier offerings.
AnandTech has a nice writeup over here.
We saw some absolute targeted performance numbers back during the February release, which promised some very interesting numbers that could be achieved over the A57. The problem was that it was not clear how much from performance and power efficiency came from the architectural changes and how much came from the the process on which these targeted performance data points are estimated from. It's clear that on the high-end ARM is promoting the A72 on the new FinFET processes from Samsung/GlobalFoundries and TSMC, which are referred to as 14nm and 16nm in the slides. Generally, due to the design and the node, the A72 will be able to achieve higher clocks than the A57, and we seem to be aiming around 2.5GHz on the 14/16nm nodes when high-end smartphones are concerned. Higher clocks may be present in server applications, where the A72 is also aimed at.