IMO, based on my 5 card rigs running on Seasonic X-850 power supplies:
Run the boards from the VGA power ports.
Run the risers from MOLEX via the peripheral/SATA ports (EVGA confirmed in a thread somewhere that those ports ARE interchangeable on the G2/P2/T2 series just like they are on the Seasonic X-series).
PCI-E slot on a riser technically can pull somewhat OVER 75 watts - 75 for the rated limit on the actual PCI-E slot PLUS losses due to voltage conversion on the riser (likely another 5-10 watts, possibly as high as 15).
SATA power connector is only rated for 54 watts of 12 VDC draw - 3 pins at 1.5 amps each (that spec is quoted from Molex, but I've seen the same spec on a couple other manufacturer sites).
You MIGHT get away with using SATA to power a riser, especially if you don't run the card on it anywhere near max TDP - but it's not a safe or sane bet if the GPU is rated for more than about 50 watts TDP.
ALSO, EVGA has said somewhere that the SATA/Peripheral ports are only rated for 75 watts - and the WIRING for those ports is pretty much NEVER heavy duty enough to support *2* risers per port on the PS anyway.
Stick with one riser per PS port for safety.
post edited by QuintLeo - 2018/01/18 12:12:32