Well PSU's generally degrade over time, so I wouldn't be surprised if your PSU wouldn't be able to pull 570w anymore
I'm not too sure how you would have to do to calculate how much your PSU has degraded however, I'm still sure it could still pump out power close to its rated wattage.
Just to be on the safe side, I would most likely replace that PSU. It's of nice quality, however, I just don't feel comfortable using a 450w PSU for such beefy GPU's. You could always use your VX450 for a different rig in the future
A lil' update, I bought and installed a Mugen 3 by Scythe and got me a new Thermaltake TR2 800W PSU.
The idle temps of the CPU went down to 25-28, and everything works much better now (new PSU installed as well), so I'm postponing the computer upgrade, as in I sold the 6950 I had and am back to the GTX 260 for the time being.