Actually, I just looked at the gtx 570 page on newegg and it says it requires a minimum of 38 amps on the 12 volt rail. The PSU I linked only provides a total of 62 amps on the 12 volt rails. I would imagine 2 570's would need at least 76 total amps on the 12 volt rail/rails. Hmmm, I'm wondering if that means you need something more like this:http://www.newegg.com/Product/Product.aspx?Item=N82E16817139013&Tpk=950tx
You should wait for more input before purchasing, I think.
EDIT: The 12 Volt rail also supplies the CPU, which at 95 Watts, needs about 95/12 ~ 8 Amps. Until you overclock. So maybe the overclocked card itself only needs around 30 or a little less. Which would mean adding another would add another 30 amps, so a psu with 68 or so amps might be fine to give you overclocking headroom for cpu and gpu.