Well the voltage dropping to 1.2498 during load from the idle of 1.312 is probably just vdroop as the processor is pulling power.
However, the voltages you see in windows; I wouldn't always trust them. Check your BIOS to see what types of voltages you're seeing in there. Second, if you're maxed out on the boards voltage; maybe you just can't toss more voltage to it?
I have noticed that different programs read voltages differently. Maybe switching to another program and trying to see what results they can give you. I use a few different ones personally to read the voltages/temps/fan speeds. The one that came with my motherboard, CPUID Hardware Monitor, CPU-Z, and once in a while I'll even pull up other software just to make sure.
Don't forget about that vdroop. My processor @ 4Ghz with 1.2v would drop to about 1.185 or so with max load according to CPUID Hardware Monitor. I don't run fixed voltage anymore so I don't have to combat with vdroop as much.
Either way, vdroop is normal. If you set to a higher voltage and the board doesn't reach it, then there is a problem somewhere.