This thread is about 40% accurate.
ALL of the data, meaning all of the A-B-A testing that I am aware of and/or have personally supervised or conducted, for every driver that such testing has been done for, strongly indicates that any 1.6L LSD (i.e. MazdaComp, Cusco) is "meaningfully" (0.1-0.3 seconds on a 2 mile track) faster than any 1.8 LSD (e.g. "Torsen"). We've seen up to 0.6 seconds on an overdriven lap with curbhopping, which is the worst case for the Torsen.
If you are not getting wheelspin with your Torsen, that's great - but you are still pulling more rotational weight via the larger 1.8L ring/pinion, and that weight is further away from the axis of rotation than the (admittedly fragile) 1.6L parts. If you ARE getting wheelspin, regardless of your LSD, then you obvisouly need to address that if you care about laptime.
Recommended use of 99-05 1.8L Torsen rear ends:
1. You have no other choice (i.e. 1.8L SM). The horrible and to-be-avoided-at-all-costs Tochigi-Fuji Super LSD is not a "choice", in my opinion. When taken apart and inspected, the T-F Super LSD appears to be nearly the cheapest possible LSD one could design - it is least the durable, least effective "clutch-type" LSD I have ever seen. I've tried to imagine how to make it even cheaper, and it was a struggle. It is the "Harbor Freight" of OEM LSDs I have seen, thus far. To be fair, I have not had an ND unit apart, but I've had NB and NC units apart. It would seem the later units survive better, but the NB units are not only ineffective, they also have a tendency to fall apart when subjected to racing.
2. You want maximum durability over speed (rental car, enduro car, you upgraded power in your 1.6L street/track car, or you are eternally midpack on a budget with a 1.6L car and you have 3 Torsens laying around and you just don't care about speed)
3. You have a street car and you want a silent, not-noticeable, non-chattery, LSD that won't one-wheel-peel *most* of the time
Recommendation for 1.6L drivers who care about laptime over durability:
1. Do not run a 1.8L (i.e. "Torsen") rear end, nor a 1.6L open or "viscous" LSD rear end.
2. Run a 1.6L rear end with a MazdaComp LSD or Cusco LSD.
3. Have a spare 1.6L rear end with you at all times - the fragile part of the rear end is the little 1.6L ring and pinion, it has nothing to do with the LSD itself.
4. "Good" (low hour undamaged) MazdaComp LSDs are getting rare. Unless you are on an extreme budget, or already have a MazdaComp LSD in your possession, just plan on getting a Cusco. I'd rather skip a weekend or stretch a set of tires than run a 15 year old MazdaComp because I'm trying to save $500-800 over a new Cusco.