That is a new one for me regarding Intel. I know they are good to go anything lower than TJmax, but this is first time I hear about 74.2°C.
My personal preference is TJmax - 15°C. Also, Intel themselves are sending CPUs to retail with fans not capable of holding those CPUs at less
than 74.2°C when loaded heavily.

Hope that is typo CPU@ 1.56v
According to Intel max safe vCore is 1.55 for Core i5.

So, you mentioned using 1.25v@4GHz? Was it stable? My numbers are not necessary if you already had stable OC with lower volts.