FX8370 has about 700MHz higher frequency (3.3 mean vs 4 mean)...168% divided by 16 threads = 10.5
105% divided by 8 thread = 13.1
So, per thread Zen is slower than fx8370 in those multithreaded apps.
Taking about 20% frequency difference it make Zen thread about equal to Piledriver in Instructions per clock?
Ofcourse, if we assume fx 8370 is an 8 core CPU and that zen CPU is also 8 core CPU, Zen is a lot faster, like 70% faster