The CX and VS series may be entry-level PSUs, but that doesn't mean they're of poor quality and unsuitable for overclocking. I have a CX 750M with an overclocked 2500k and it hasn't put a foot wrong.
The VS650 delivers 600W on its single +12V rail, so it will be fine for overclocking, but not so fine for Crossfire. If you're planning to do that, you should look at 750W minimum. The wattage you need depends on which specific GPUs you want to Crossfire, but 750W is a good ballpark figure.
What if i didn't use for Crossfire / Overclock it ? Just use on some GPU like GTX570 / HD6870. it is okay for it? will it come error or any problem?