According the the Mk1 GS300 Sport brochure I have, it says the suspension is lowered by 25mm. It doesn't give a different figure for front and rear so I guess it is the same all round.
The previous owner of my Sport had raised the car due to the design of his driveway, so I've had to reverse that. I didn't bother with OEM springs. TDI said they could get some lowering springs with a lead time of 4 months or something unless you went for the airmail price which was too much for me. I ended up ordering from Envy Performance. Transaction wasn't totally smooth mind you, their acquasition time was much longer than they first said. I ordered the Espelir Active Super Down springs with 30mm drop, however when the springs did finally arrive, the japanese supplier had sent the wrong items and I got RS*R Down springs instead. Had no problems with them so far, although I have the rears to fit still. When the new ones went on the front, the ludicrous camber introduced by the high springs and the geo not being redone was instantly sorted.
Best shots I have on the pc at the mo are these ones to show the front arch and stance of the car.