you have to check Bitstamp rates on blockchain.info .
I think this was the rate when I checked there

BITSTAMP    $582.53
high:$ 595.70 low: $581.80 avg:$ 587.68

but if I will buy Bitcoins in exchange of Perfectmoney then I will prefer BTC-e . there is always a difference in rate

BTC-E    $576.59
high: $588.88 low: $576.00 avg: $581.44