Overclocking on Asrock Extreme4 Z77

[Endymion FRS]

I'm just going for a mild overclock with an i5-3570K, like 4.2. When I set the Turbo to 4.2 in the bios, voltage jumps to 1.275 under full load, is that normal? I was just going for the highest I could do under stock voltage, and that's higher than stock. I don't see anywhere where I can limit voltage.