DDR3 ram is rated at a standard 1.5 volts.
In order to run DDR3 memory at faster speeds, most companies require you to increase the voltage to the maximum allowable 'standard'. That is, 1.65 volts.
The P55 motherboards all support increasing the voltage to 1.65 volts, although the Gigabyte BIOS will show 1.64 - which is fine.
One point of note: to run that G.Skill memory at rated speed [1600MHz, at 7-7-7-24 (2T) and 1.65V] you will need to enable the XMP profile (under BIOS Memory menu), or enter the timings manually.
Also, if running a Core i5, this will overclock the CPU base clock (frequency) from 133 to 160MHz, due to the limited x10 memory multiplier integrated onto the processor.