First, let's ask some preliminary questions.
What are you cooling the CPU with? A stock OEM cooler or a good aftermarket cooler? Make and model please if aftermarket. Overclocking requires good cooling because the CPU will run hotter. Pleas make us a list of your hardware to include additional items you have not revealed such as PSU make and wattage and video card. You can use my "Sig" for guidance if you like of the info we like to see.
For the same reason, what is the make and model of your case and how are the fans arranged as far as intake and exhaust?
Have you done any stress testing and temperature monitoring to get a baseline for temps? You are already running a core voltage of 1.425 and I don't think you will be able to add to that very much during overclocking because of temps.
Please download and install: CPU-z (for reporting frequencies and bios setting information) , HWMonitor (non pro version, for reporting temps and voltages) and Prime95 (an older version like 27.7 or 27.9) for creating a load on the CPU.
Open HWMonitor on the desktop and leave it open while you run the Prime95 "blend" "just stress testing" test for 20 minutes.
Post back with a pic attached of HWMonitor that shows the core/package temp section. To attach a pic, click on the Go Advanced button at the bottom right corner of any new post windows. That will start the attaching tool. Use Snipping Tool in Windows Accessories to crop and save the pic first.
