By the way your Tahiti's are running too slow, you should modify the bios and you can get almost 300 H/s out of your 7970/280x.
https://bitcointalksearch.org/topic/hacked-modified-memory-strap-bios-database-for-zec-mining-1676474
Alot of labour however.
Also why don't you mine XMR instead with your Pitcairn's, I think they produce more profit than ZEC.
EDIT: I see you mine XMR on all your 370s in the other rigs.
Why don't you dual mine ETH+DCR for your 480s instead you do XMR, I think the profit is lower.
The problem is temps/heat, all the 280x are undervolted, they dont clock high enough, i wanted to sell them to get lower TDP cards, so i didnt want to bother modding them. But since people are being silly/stingy about investing into GPUs, i may do that if i expand instead.
The 480s are on XMR for temps reasons as well, i don't know if its a configuration issues but dual mining on my RX when i tried was massive loss on ETH hashrate.
Its funny you linked that to me thought, i was asked not that long ago to do that mod for 290s. But seeing how people arent interested in 4 months ROI, i think i just might.