  We present charm and bottom nuclear modification factors for RHIC and LHC
using Standard Model perturbative QCD and recent AdS/CFT string drag energy
loss models. We find that extreme extrapolations to LHC mask potential
experimentally determinable differences in the individual $R_{AA}$s but that
their ratio, $R_{AA}^c/R_{AA}^b$ as a function of transverse momentum is a
remarkably robust observable for finding deviations from either theoretical
framework.
