A significant jump, if true.
AMD hasn't officially announced anything with regards to the next generation Radeon HD series. We know it's coming, but there's no official word on models, specifications or clock speeds yet.
What we do have are potential leaks and the speculation that comes with all of that. This chart has been leaked from two different sources showing the performance leap that will come from the Radeon HD 6700 "Barts" series. It's all unconfirmed, but we certainly hope that they're true, given the claims of significant performance improvements.
The chart below comes from Napoleon of ChipHell fame.