As fast as motherboard gets hot (in speccy)
How hot is 'gets hot' ? Depending on the processor installed Speccy may report either the core temperature or the motherboard temperature or both.
As a guide, processor temperature should NOT exceed 75-80C (175F), motherboard temperatures probably should not exceed 40-45C (110F). For reference, Speccy gives the current temperatures for my system as : motherboard - 28C; graphics processor - 61C; hard drives - 26C.
You may have a cooling problem. You say you have cleaned out the CPU box - I presume you mean the heatsink assembly. Are you certain the fan is working ? If the fan is working, then it the thermal paste between the processor and the heatsink may not be forming a thermal bond and need replacing. Are all the other fans in the system working ?