Because Deneb has a very robust FPU. The problem is that it's not multithreaded so it loses to i7's SMT capabilities in MT aware software.
Bulldozer remedies this somewhat since it has 4 FP units that are 2 way SMT capable. That's why "8 core"(integer core) Bulldozer has a ~SB level performance in FP intensive workloads. 4 FP units vs 4 FP units,both 8 threads capable.
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