Based on your statement:
Based on the above, the difference in wattage between my 5 and 6 card rig was 130 watts while using a 115 watt GPU power limit. I verified the GPU power consumption on my power monitor and in the driver settings. This equates to a PSI riser consumption of around 15 watts. Since I was running these on the 12V rail this is a little over 1 amp. I noticed when I increased the card power that riser consumption did not change. Perhaps i can re-run the test at higher power limits to see the effects.
Even though the test shows that the power consumption is fairly low, you need to confirm your power supply can handle the load demand based on what connector you are using. In my opinion it is best to power risers from the 12 V rail with a PCI power cable or a molex cable (both run off the 12 v rail). SATA is not really meant to power risers and i'm no even sure why they design risers with this option. Since they use 3.3 V rail this increases the current to about 4-5 amps (15 watts / 3.3 V = 4.45 Amps) per SATA power cable. Based on the specifications below, if you are powering 5 risers from the 3.3 V rail you will be exceeding the rail power limits (4.45 x 5 = 22.7 Amps) which can damage the power supply or catch it on fire. So in conclusion, power your risers with INDIVIDUAL (not daisy-chained) PCI power cables or molex cables and you should be okay. PCI and molex cables both run off the 12V rail and this rail can handle the highest power demand.
Mean one SATA rail was powering one Risers is okay right? I've never tried to measure how much power would draw by GPUs from a Risers, but based on my experience one SATA rail powering one Risers seems safe.
I've got this kind of discussion before. About how to powering the Risers. You have to use more than one object for each part for a more accurate result, IMO.
A different card may be draw different power from the Risers, each card has different power management, and we have zero control on that. S different PSUs have a different specification in power producing.
Overall, I like what you do, keep going!
my first rig has been running for MONTHS in the perfect storm of "bad" configs. 8 GPUs, V006c risers (6-pin power) using SATA->6-pin adapters. running 2 SATA cables from the PSU, with 4 risers on each line (from a very high end 1200w plat PSU with metal barrel connectors). it's fine *mic drop*
the biggest problem is getting enough 6-pin connectors in most cases.
Same as you, I'm using SATA for more than one years without issue. One SATA rail / Risers seems fine for me.
PCIe cable (8,6+2,6) will more useful for powering GPUs.