Throttling limits the speed of all services and protocols (i.e. the overall speed of your internet connection).
Regardless of the line speed, a throttled account will only be able to achieve limited speed when throttling is applied. The line itself is not affected, and using an unthrottled account will return line performance to normal.
Throttling is applied on an individual per user basis, based overall usage within a given month. Throttling is only ever applied when demand on the network exceeds available network capacity, and is de-activated when demand returns to normal levels.