The problem with undervolting is that it might crash every few hours or so. And you have to manually restart the mining.
not to mention removing the warranty with all those bios flash, i would certainly not do it with so many gpu, the risk to screw one is high, and those card are expensive, it must be said that without this mod, having 1500w for 170 mega on ETH, is not good at all, a 970 can do 1k and 132 mega, this is almost 200 mega with 1500w
yes but some considerations are; max gpu per rig and ability to resell gpu's when mining goes PoS or unprofitable.
nano's smaller form factor make them pretty desirable for some scenarios, even when newer and more powerful gpu's are out in the wild.. the 970gtx is already the little brother to the 980.. not sure it would fetch the same price in 18 months time.