(Sorry for the necro, but thought I should ask here given it's quoting people's comments)
What would be the harm in splicing in connectors from another cable? I have a leftover 6-pin Cablemod Pro PCIe power cable that I want to convert into an 8-pin (full wires, not the GPU connector side-wires extension) by cutting and splicing together wires the Molex cables from my set that I don't use. Because they're shorter than the 6-wires of the PCIe 6-pin, I'll have to splice together two halves per wire (which will already have the original female connectors attached). Mind you, this is only for the extra Sense+Ground wires, so no current will be flowing over them.
If I'm cutting and soldering the same cables from the set -- thus wire/shielding properties are all the same -- would it be a problem if I solder-spliced leftover cables to make these two Sense/Ground PCIe wires? I want to make these two wires the same length as the other 6. I'm also extremely proficient at good, clean soldering. But perhaps I'm missing something as to why not to do this.
What about a quality solid soldering station like Weller WES51? Surely that would be able to solder cabling such as this?