Was there any particular reason you chose the dead and obsolete Socket AM3 platform instead of the far superior Socket AM4? Also, 114.5MB/s is butting up against the typical sustained write speed of a hard drive, especially if you are reading and extracting the archive on the same drive. Also, the FX-8350 is a 4 module 8 thread processor so it still only has 4 floating point processors.
As for performance benchmarks, there's no shortage of them, but there's also no universal benchmark as each one is situational, even Linpack has its detractors, which is why reputable review sites focus more on a suite of real world applications, not premade benchmarks. So the answer to your first question is there is no way to obtain the "true" computational power of a machine because there is no "true" computational value, especially when it comes to multithreading because not every program will utilize it in the same way, some do not at all, some achieve nearly 100% scaling, and most fall between those two values.
As for the motherboard, it has little to do with the computational speed outside the supported RAM speeds, overclocking ability, and drive interfaces, but if you take two motherboards, one an entry level model, say a AMD 960 chipset board, and one a high end model, say the ASUS Crosshair V, stick the same CPU, RAM, and drives in there, raw computational performance will be equal.