Ok, it seems that the GTX 1060 is not really a good choice for Ethereum. I'll wait for the RX 570 or 580 (I don't know if 4 or 8 gb, it depends on what I will find) . Which is the best rig config for these cards? I mean, motherboard, cpu etc?
Depending of the number of GPU...
For a RIG of 6 GPU you can use:
Mother board: H81 Pro BTC R2.0
CPU: Intel Haswell Processeur Pentium G3260 3.3 GHz 3Mo Cache Socket 1150
But to be simple CPU is not use at all during mining process so a small one is enough.
For disk it gonna depend of the OS. For a linux USB key 8g is enough but for windows SSD 40g is require.
Memory 4G is enough for linux 8G is better for Windob.