Now, the need for voltage increase is case by case basis. You can keep the CPU Voltage at Auto if you are still at the stock clockspeed. You can test stability of your new X4 by running SuperPi or intelburn test as these are the quickest way although admittedly not the most reliable indicators. For superpi, run for up to 32M and you can get result in around 20minutes at your clock speed. For Intelburn test, run 10 runs of standard test or if you want more stability do the test on High.
If you pass these tests, then it means your X4 is stable for not very stressful situation ( like playing games ). You need to increase the CPU voltage only if you fail in these test. It will not harm your processor to have CPU voltage up to 1.425v as this is well within AMD recommended max CPUvoltage.