I'll take a stab at your question as to how the 7MM BR compares to the 7MM-08 Harp. Basically you just have to ask yourself how far you intend to shoot these whitetails. The 7MM-08 will shoot farther and flatter than the 7MM BR at the expense of extra noise, powder, blast, and recoil.
I am an efficiency nut and like matching cartridges to the size of the animal and the ranges which I will be shooting.
HTH,
X