For-aft adjustment of the VO saddle is affected more by the setback of the seatpost than the length of the rails. The rails are a bit longer because they are more squared off at the rear and they narrow closer to the front.
I just physically compared my VO saddle with a Brooks. The rear of the rails end in the same place on both saddles. All of the difference is in the front of the rails. So the short answer is that a VO saddle doesn't go any farther forward than a Brooks, but should go about a cm. further back.