Finally I found some data on the internet for S7 and 52100. But I don't know how accurate and relevant it is, especially SR-77 and SR-101 might differ a bit from S7 and 52100.

Here is what I found:

S7 shock steel
It seems critical temperature starts at 710 °C 1310 °F , but in industry is "suitable for hot work tools where the operating temperature does not exceed 1000°F (538°C)".
I can understand it can be even used at 538 Celsius. I'm not a metalurgist, so I'm not sure I understanded well. And I'm not sure SR-77 behaves exactly the same. If I missed something, please someone correct me.
http://www.matweb.com/search/datasheet.aspx?matguid=639809fb26c348c18feb498607d21e64&ckck=1

52100 steel
"Tempering - Temper at 400 F" (this means 204 C)
It seems huge difference compared to S7... I might not have understanded well <img src="/ubbthreads/images/graemlins/confused.gif" alt="" /> . Please correct me if I didn't understand well.
And again, I don't know the difference between 52100 and SR-101 and I don't know how much they behave the same.
http://www.suppliersonline.com/propertypages/52100.asp

Regarding INFI, I couldn't find anything in regards to its temper limits.


Nothern1, are you talking about degrees Celsius or Fahrenheit? If it's Celsius, it is a huge temperature, seems unbelievable. If it's Fahrenheit it seems SR-77 is above it in that regards.

Depends on how the steel was pre, post and heat treated, how the steel was machined afterwards and where the maker wanted the mechanical properties of toughness and wear resistance to lie.