Depends entirely on the code as to how well they take advantage of it. If the code doesn't move the extruders at the same time as the axes (ie: if there is some other code in between), then it's not going to help at all.
As to ARM, yes, they're faster, but even then there are limits, especially if you decide to increase microstepping (I saw someone mention wanting 1/64th recently).
As to ARM, yes, they're faster, but even then there are limits, especially if you decide to increase microstepping (I saw someone mention wanting 1/64th recently).