That's pretty much irrelevant since the AMD's FX arch's issues weren't that SW at the time wasn't using all the 8 cores. Intel dropped the Core 2 Duo and Quad into the era where most SW was still stuck in single threaded for a long time and those CPUs still ripped single-threaded SW tasks regardless.

Here's the big reasons why the FX sucked back then and why they still suck today in the multi-thread SW era:

  Instead of discrete, fully independent cores, AMD grouped processing units into "Modules" where each module contained two integer execution units, but they had to share critical resources like one FPU, the instruction fetch/decode pipeline, and the L2 cache so when both "cores" inside a module were heavily taxed especially with math or physics-heavy calculations (like in videogames), they choked fighting over shared hardware.

  AMD designed Bulldozer with a very long pipeline, betting they could sacrifice efficiency per clock cycle in exchange for extraordinarily high clock speeds(a-la Intel Pentium 4) but the IPC was so bad that an FX core was often slower clock-for-clock than AMD’s previous-generation Phenom II chips and also their power consumption exploded. 

  FX processors were plagued by high cache latencies and an inefficient memory subsystem as another bottleneck.

Last year I picked up an e-wasted FX PC for nostalgia tinkering and boy, it definitely feels veeery slow today, even on lightweight modern Linux regardless of having as many cores as modern CPUs, the arch is just that bottlenecked, and when you add the missing modern instruction sets such as AVX2, FMA3, and modern security extensions, they only contribute to the slowness in modern use cases compared to today's CPUs that beat it while using much less power. It's fine as WindowsXP era PC for retro gaming I guess, but even then you can do much better with and Intel PC from the same era that's gonna be way less power hungry.