[rallyhub]

So how does powered, forward facing front wheels benefit performance? 

Surely on every bend in the track, they will be fighting against the guide which is trying to drag them round the corner? Or do the wheels steer?

Uphill and at the end of a bend:
Uphill is clear; grip from two extra wheels.
At the end of the bend, the driven front wheels pull the car out of the bend; avoiding too much oversteer.
You have to keep in mind, that a rally track is more twisty and often steeper than a race track.
Magnets are not done on a rally track.
At the beginning of a bend you lift the throttle to avoid understeer.
In the bend the tail will come out, starting a nice four-wheel powerslide.

rallyhub