I have 2x 6 GPU R9 280x rigs that I built. (1 is Sapphire Toxic and the other is Sapphire Vapor)
Each card gets a little over 300H/s on ZCash using Claymore 12.3 miner. I would say between 290 and 310 H/s is typical.
So in other words its better to go beg for change in the street than mine ZCash.
Awesome.
Depends on several factors.
1) What you pay for power
2) What you pay for other hardware (PSU, MOBO, ETC)
3) What you pay to acquire the GPU's
4) What the resale value is of the acquired cards
I have a rig with a couple of 7950's. It is using older hardware I already had so no additional costs there. I picked up a sweet deal where I can resell them for a higher price then I acquired them. For me they ROI within 2 months if I use a resale value of €0,-. So it's win-win.