After a quick google search, i learned that FX series CPUs have very poor thermal reporting functionally, generally the chips report 5-10 (and in some case, 20) degrees hotter than they really are.
And FX CPUs (like me) instead of using a direct contact thermometer uses a algorithim to "guess" the temperature, is true?
Yep they use math to guess the temperature, this is done to provide more accurate temperature readings over 45 degrees centigrade than a motherboard thermal diode will (the hotter they get the less accurate they are), below 45 it's not very accurate at all (hence some people seeing temps at 0 degrees even in a warm room).
AMD's overdrive utility shows the thermal margin between current temps and thermal throttling (62 degrees) and it's the ONLY software that properly reads temps from FX cpus (all the others try to read it as if it were actually a physical temperature, which is why they're not very reliable)
So to have a "real" temperature should I use "AMD Overdrive"?
By chance while playing you can see the results as MSI Afterburner programs?
If you're talking about the CPU Socket Temperature then yes, but there is no reason to use that temperature, what you want to use is the CPU Core Temperature. They inaccurately report temperatures below 40°C, but that's not really an issue.
I ask this question becuz i know (see on site AMD) my CPU can resist 61° degrees, and playing FALLOUT 4 sometimes the CPU say "65° degrees", i scary this kill my CPU. :\
As I said it depends on which temperature you're reading, the incorrect CPU socket temperature or the accurate CPU core temperature. AIDA64 and Coretemp show the correct core temperatures, AMD Overdrive shows a useless thermal margin number. Even a quick stability test shows the reported CPU socket temperature to be 4°C higher than the actual core temperature, and I use a high powered Corsair H105. And the thermal max is the highest temperature which it is guaranteed to work without errors, you'll get memory read errors and BSODs long before the heat actually causes any damage.
So I do not worry? If the "MSI Afterburner" program tells me 65 degrees is not it, and the actual temperature is less than 65 degrees?
If I understand correctly what you want me to say.