Do good power cords have to be stiff?

I have made PCs with Oyaide Tunami V2 bulk cable that sound good but are quite stiff.

I have also made PCs from NOS Western Electric 10ga wire, both in 10ga and 7 ga configurations that sound good and are reasonably flexible too.  The NOS Western Electric 10ga wire is also used by TWL in their American 10 and 7 PCs, and was used by previously by Mojo Audio in their well-regarded PCs. The stuff makes nice speaker cables too.

I get that 12-14 awg should be enough wire for most components, but when I plugged in my 650 wpc monos using the 7 awg WE PCs it was one of the few times  I perceived that cables went beyond simply making a difference to making a definite improvement.  The 7ga cables are 6 runs of 10ga wire into each Furutech FI-11 connector, 2 runs each for pos, neg, and ground.  The 10ga version are more flexible and certainly big enough to handle any audio related load, but for some reason it seems the bigger 7ga cables sound even better on my big amps.