The car compares favorably with the new M157 twin turbo V8 based 63 AMG cars from Mercedes. Motortrend tested a performance package version of the CLS63 AMG at 12.1@121. The E63 AMG however is lighter than the CLS (which the new M5 weighs almost the same as) and also has the performance package available so it is likely that it will be close between the E63 AMG and the F10 M5 stock with the edge likely going in the E63's favor with the performance package.
It will be interesting to see which one will be faster with a tune as the performance package does not leave much to improve on. In this respect, the M5 should have the edge when power is added also considering its faster transmission. Either way, we have a heck of an epic battle brewing that will go back and forth for some time to come.