the bigger diff (3.27) will use more petrol because it revs higher at 100km/hr than a 3.08.. My 3.45 LSD revs at around 2150rpm at 100km/hr while a GL with a 3.27??? or 3.08 (not sure) will rev at around 1700-1800..
On the dragstrip, the 3.27 should accelerate faster if the two cars were identical , conditions were the same, same driver etc, but we all know this doesn't happen...
All in all, the bigger the diff, the more fuel and faster acceleration.. The XR6 i have (EF) all came out with 3.45 LSD's..