After i tried everything, before to become crazy a few days ago I did the only thing i could do, solving the problem: i sold gigabyte and i bought a "level entry" asus P6T.
Now i'm going 201x19 @ 3815mhz. vcore 1.29 from bios. 1.28 in idle in windows. 1.296 in full in windows after 3 hours of LinX. Vcore is solid as a rock, it doesn't move from there.
And now i can sleep, finally.

ciao!