Piledriver still has a lower IPC than Phenom II. I owned a 1090t and ran it at 4GHz. When I upgraded to an FX-8320 (rest of the system stayed the same) and ran that at 4GHz, it was noticeably slower in all single-threaded benchmarks. I even lost the multi-threaded test in Cinebench R11.5. It made up for this by being able to reach a much higher overclock (4.8GHz+ for the 8320 vs 4.1GHz for the 1090t), but it still only ended up breaking even on single threaded benchmarks. I dug up my old test results:

Phenom II X6 1090t @ 4.0 GHz and 7870 @ stock clocks:
3DMark06:
Overall Score: 22421
CPU Score: 6717
3DMark11:
Overall Score: X2401
Physics Score: 5515
CineBench R11.5:
CPU Score: 7.03
FX 8320 @ stock clocks:
3DMark06:
Overall Score: 18984
CPU Score: 5683
3DMark11:
Overall Score: X2395
Physics Score: 6617
CineBench R11.5:
CPU Score: 6.05
FX 8320 @ 4.0 GHz:
3DMark06:
Overall Score: 20420
CPU Score: 5994
3DMark11:
Overall Score: X2396
Physics Score: 6868
CineBench R11.5:
CPU Score: 6.88