I have an i5-4440 with a P81-D3 MOBO
both of'em is supposed to support Intel Boost Tech i also made sure that the boost is enabled jn the BIOS but even when my load reaches 100% the cpu remains working at 3.04~3.07 GHz
I've used MSI CPU Burner to load the CPU , And CPU-z , HWinfo , Task Manger to check the freq.
And it never went higher than 3.07
PS: the temp never go higher than 60 c , I'am using 8-Pin Connector for the cpu power socket on the mobo
I suggest that your run the Intel Processor Diagnostic Tool, if you find that the turbo feature is still not working, you would need to check your motherboard settings since this would be controlled be the motherboard and not the processor. You can check with the manufacture to see if they would recommend a BIOS update or some other fix.
Intel Processor Diagnostic Tool: