Computer temps are usually discussed in Celsius. Not sure who is using Fahrenheit.
A good way to gauge your card temps is by looking at review sites. They typically have a temp chart. Tom's doesn't seem to have one for the 570 review, but Anandtech did. Under load playing Crysis it hit 82C. Running FurMark 88C. According to Nvidia's site the MAX GPU temp is 97C.
http://www.anandtech.com/show/4051/nvidias-geforce-gtx-570-filling-in-the-gaps/15
What I take from this is typical heavy game temps will be low 80's, 80-84C for heavy GPU games. For benchmark stress tests I would expect high 80s, 85-89C. Anything over these temps I would start to be concerned. Just remember this is on a completely stock cooled card. These may vary depending on how the manufacture sets the fan profiles or if it has an upgraded cooler. Some are more aggressive than others in this area. So if one person has an ASUS and says, anything over 75C is bad because I never go over that, might not apply to someone that has an EVGA with a less aggressive fan profile.
I tend to set my profile manually and be a little more aggressive at higher temps. I am using MSI afterburner as it has a nice fan adjustment.