I don't have figures to back this up but having many miles on the 53 and just 18000 on the 70 my seat of the pants says the 53 may be better. They are both about the same on the highway and my 70 is worse around town. Can't say that for all the X's but for my cars thats the way it shakes out!

__________________
2008 E-70 4.8 Titanium Silver Met/Black/Bamboo