This is a difficult set of questions to answer with any consistency. Results will vary from one processor generation to another, from one individual processor to another, from one platform (and BIOS configuration) to another and from one O/S to another. It depends upon the power management features that are enabled, the processor cooling solution that is utilized, the fan speed control configuration (typically in BIOS) that is utilized, etc. and etc. and etc.
So what are you aiming for? Well, if you are talking about a standard Desktop processor, in a standard form factor motherboard (ATX/uATX/ITX), in a standard mini/midi/full tower chassis, with a standard (heatsink-fan) cooling solution, running a Windows O/S, you should be aiming to have an idle temperature in the 35c-50c range. With a liquid cooling solution, you should be able to move this range down to 30c-40c. However, if it's Windows 10, with its plethora of background tasks (and spyware), expect it to be difficult to maintain even the high-end of this range).
When running benchmark-level software - like Prime95 - you should be aiming to have the temperature stay around (at or below) the processor's Tcontrol temperature with only the odd (but short duration) spike above this threshold. This requires that the processor fan speed control configuration ensure that, if the temperature is above the Tcontrol threshold, the fan(s)/blower(s)/pump(s)/motor(s) involved will be at their maximum speed (i.e. 100% duty cycle).
[Aside: for Desktop processors, the Tcontrol temperature threshold can be obtained by reading the IA32 Temperature Target Model-Specific Register (MSR). It's address is 0x01A2. Bits 16-23 specify the processor's Maximum Junction Temperature (Tjmax) and bits 8-15 specify the Tcontrol offset. Subtract the Tcontrol offset from the Tjmax value to get the Tcontrol temperature threshold. To read MSRs, you need a special program. One (Windows) freeware program that can do this is RWEverything.]
Hope this helps,