At a certain point in OCing the CPU, RAM, memory controler and chip set may require increases in voltage.
RAM, as I said, a few tenths of a volt, that is a safe increase and will help the RAM to run higher speeds.
CPU, several things to consider, how much, only 0.1v increases at a time when you hit instability but do watch the "Full Load" temp when testing with OCCT or Orthos which will full load up the CPU and heat it up. The MAX Full Load temp is considered @ 50c and preferably no higher when OCing.
The HT... or "LDT" on a DFI MB
That is the memory, it's base speed which is the CPU's OCed speed multiplied by the memory controler. Here is how it works.
The CPU speed is 200 @ default or stock speed, it's multiplyed by 5 for a total of 1000. Remember this, some where around the 1200 range is getting to high and causes instability (preferably keep it under 1100) so...
You will likely only see an HT or LDT of 5, 4, 3, and 2 in the BIOS
The CPU multiplyer will likely be 10, 9, 8, 7, 6, 5,
Once the CPU is OCed to about 260 use a 4x for the HT or LDT. Above 2160 frop down to a 3x.
The HT or LDT multiplyer is not the "CPU" multiplyer so dont confuse them.
Later you might need to increase the memory controler and chip set voltage but for now don't worry or bother
BTW, if you don't have CPU-Z, do get it @ www.cpuid.com
because it's handy and will show you the HT (LDT) CPU OC speed and RAM speeds and timings!