Handling with improve as you will be able to put more power down whilst exiting corners due to the better traction a LSD offers.
Mal will correct your Speedo with a gear that suits so that isnt an issue.
Acceleration will improve a bit, BUT I have experienced huge torque limiting from the ecu since doing 3.9's in a Au2 xr8 auto. I dont believe the I6 is limited as hard as the 8 though after in depth discussions. So the gain will be there for sure but an EDIT will be advisable in the not to distant future to get the most out of it. (Should be available just after christmas at this stage i believe)
If yours is an auto your speed limiter will be lower than before (not really an isssue unless its for track use J3 chiptorque or Edit will fix this)
Also your shift points Eg where the auto changes up, may differ a little bit but should still be drivable. Once again an edit or a chiptorque j3 program can fix this.
Bear in mind your rpm at 100kph will increase and I would say that 3.9's in a i6 would put you at a guess around 3000rpm. (ask OED666) Meaning more fuel usage. But anything around 2300 should be ok ask Mal about this.
Clunk will be compltely gone provided its the diff as Mal and Ben will completely rebuild it. Make sure the noise you are hearing isn't your tail shaft.
Speaking of tailshaft I'm not sure what they are like in the sedans but the utes need a 2 peice one as the factory 1 peice item is a nasty bit of gear
I hope thats helped you out a bit and please feel free to correct me on anything I didnt get quite right