Wait a minute ?? to my knowledge they all have Limited Slip Diferentials. But there are center LSD's which splits torque b/w front and rear in AWD's and and rear/front LSD's which split torque b/w left and right wheels (RWD or AWD), and also different types of LSD:
- 996TT has a "viscous-coupling" type Limited Slip Differential in the center to split torque b/w front and rear which makes it AWD, but has no front or rear real mechanical LSD, instead it uses the Automatic Brake Differential (ABD) which is an electronic differential instead in order to be compatible with the PSM.
- 40th aniversary 911 doesn't have a center diff because its RWD not AWD but instead of the ABD of the current RWD 996's (except GT3/GT2) now has the a traditional mechanical differential lock LSD in the rear and is finally compatible with PSM (GT3/GT2 have differential lock LSD hats why they couldn't have PSM). The E46-M3 is RWD too and has a viscous diff for example, and the E36-M3 had a differential lock type like the GT3.
- Impreza/Lancia Delta Integrale/Ford RS cosworth/Lancer EVO (euro spec) types have a centre LSD's like the 996TT since the are AWD's but instead of being the just viscous coupling LSD of the 996TT, its a combination of the traditional mechanical differential lock LSD and the viscous-coupling LSD, called "viscous-coupling differential lock". Besides this centre diff they also have rear & front mechanical diff's (unlike the 996TT) of the viscous or torsen type to futher improve grip. Giving them the excellent traction/handling in various surface conditions.
So as I understand it, the AWD 996's have LSD of the viscous type in the centre and none at the rear and front except for the electronic ABD. Now with these news that diff lock is compatible with PSM we could expect the future generation AWD 911's to have also LSD on rear axle as well as the viscous centre to improve its handling even further because mechanical LSD's are sportier, less intrusive that electronic differential like the ABD or Audi's Haldex system, just like the rally based impreza/Lance EVO, etc. So it would make sense to add mech LSD's to the AWD 911's at least rear axle?
The torsen (audi's "quattro" in A4 and up) is the really heavy differential which, is permanent and instant acting compared to the others, but does not permit variation in the torque rear vs front which is permanently set to 50:50 therefore not very sporty and handles like a FWD car but great for grip in slippery conditions. This is the one that doesn't make sense in sportcars IMO.
If I missed something or gotten it wrong please correct me, I'm not an expert at this and I'm here to learn