One thing I do wonder though, is there any danger of voltage differentials, ex: one psu's 12v rail might be 12.1 while the other might be 12.3, will that actually cause some weird 0.2 voltage difference/loop that could blow components? Inputs are more than likely just going straight to a buck converter anyway right? Can't really tell for sure by looking at a GPU as most of the components are hidden but I do see some components that point towards the possibility of a buck converter. To be safe I guess it's probably good to power the riser and the card itself from the same PSU, as the risers take their own power anyway, which is good, so no power is traveling over the USB as far as I can tell.
Kind of getting excited to build my real rig. Having the card jerry rigged in my gaming machine with the case cover off is kinda annoying. I will build my rig's case as 5U so the card will fit. 4U does not quite cut it.
Also managed to score another 1070 off ebay at a half decent price. $800ish. Not too bad considering I paid over $700 for the first one, at retail price.
At this point ROI is kind of far, so I really need to stop spending money on this. But I see it as a fun project too, also not really considering the cost of the rig components, as I can easily repurpose that. I'm hoping I get a nice tax return this year as it will help pay off this stuff.