done this mod on my 99 agu as the bushes were worn and needed doing, so i bought both bushes, small and big, put them both on which solved my issues with a slumpy rolly engine.,,, but at the same time gave the most horendous vibration in the car! it did improve the response time slightly and made it feel more direct but in short i have a new born baby and i hate rattles.... so it had to go, ordered myself a used perfect condition mount complete with buses and its lovely! i stil have the original bushes as i was going to replase the upright round (small) one as i think just this alone would give a happy medium.
i still have the whole mount together ready to bolt on for sale if anyone wants it tho.. i only changed it back for comfort reasons, 3 years ago and i wouldnt have cared!