Both the Soldier's and the Vanguard's unique abilities (Adrenaline Rush and Charge, respectively) create the illusion of shifting the user's time-reference point relative to the opposition (meaning that what the user perceives as everything slowing down, the enemy perceives it as the user speeding up [or vice-versa]). But which power, from a normal timeframe point of view, is faster?
Here's how I see it...
Normally Adrenaline Rush has a time dilation factor of 50%, meaning that all motion appears slower by 50% of actual speed from the user's point of view, but 50% faster from the opponent's point of view. Heightened A.R. has a time dilation factor of 70%. This means that the enemy would perceive Shepard as moving 70% faster than normal speed, giving an illusion of super speed.
Meanwhile, Charge temporarily slows the reference point of Shepard's surroundings to the point that the enemies seem to stand still, then after powering up, he/she then blasts toward the enemy at super speed at the normal frame rate, while in Shep's reference point it could be that he/she is simply running and defying gravity. When upgraded to Heavy Charge, impact results in further time dilation, enough to pull off a few shotgun shots.
If this sounds confusing, I apologize off the bat... I'm not well-versed in physics, especially relativistic physics, but i'm giving it a shot here.
Personally I think that Charge is faster, since it seems to move at least triple the relative speed of a user of A.R.
Now what do you guys think?