That would be me. I've got two of those Rosewills - the review unit will be pushing a 6 card rig as soon as I figure out what I'm doing for a motherboard.

Seasonic has been 18 AWG on all cables for a while now. I'm trying to gently prod them into upgrading those PCIe cables. They're amazing PSUs, but not what I run in the dedicated mining rigs because they're not really intended or built for it. That said, I have a Prime Titanium 750W running the office rig, and it does mine. It uses two single connector cables to push one downvolted 290X to get around the wire gauge issues. I've also got a Seasonic 1050W mining a three card machine temporarily until I un-lazy myself and get that Rosewill in there. Again, using as many connections between the PSU and GPUs as possible.

I actually can't remember the last time I saw peripheral cables bigger than 18 AWG, actually. Even my Super Flower 1600s use 18. That said, I usually run two risers per cable and have never had an issue provided I use them with cards that don't take a lot of slot power. For cards that do pull a lot from the slot, I get the risers with actual PCIe power connectors on them. You don't want to pull 90W out of one Molex for 24/7 use.