Yes, going from a 6850 to a 7970 yields a 3x improvement in Luxmark V2.0 running on open cl 1.2
However, FAH yields a negative, ie. a 7970 does not work as well as the 6850. Running the same (open version) Opencl program.
The difference is attributed by the programers to a lack of robust drivers compilers on the part of AMD...ie. the functions supported on the previous compiler stack are not now supported/optimized to run on the new open source stack.
FAH cores themselves are not open source. Mike Houston could give you some insight as he was actively participating at one time.
But thanks for responding even though you have no immediate experience with the issue.