Yeah vdroop is the voltage difference between idle and full load.
Vdrop is usually considered to be the difference between BIOS setting and BIOS readout, although this is not accurate because the BIOS actually puts a small load on the cpu. (you can tell by comparing BIOS temps to idle temps).
So Vdrop is the difference between BIOS voltage setting and idle voltage.

Whether the poster's chip can boot at 0.86v depends on its default vid, I think...it's possible a 1.15v vid chip can load windows at .86v, but I sure wouldn't think it would pass prime.

As Yolanda said, a VERY good test is to check load temps.