Differentials are an entire world of their own. I feel like I could spend 5 years researching diffs and still not make a fully-informed decision
Cusco: MZ-vs-RS-vs-Hybrid? And given it's easy to customize before I put it in for the first time, any reason to re-arrange the disks for less-than-full lockup, etc?
OS Giken: reputable, pricey, solid option, not much else to say?
Nismo: GT Pro - Even more expensive than OSG, somehow? Their marketing materials do sound nice, but I don't know if it's that nice.
I had decided a while back (just based on internet research) to skip over the Quaife just because the one-wheel-lift thing seems shitty, and as I get further in my suspension setup, that scenario gets more and more likely. But now I've noticed that there's another torsen type called WaveTrac that claims to be very similar but eliminates the unloaded-wheel problem. That makes me wonder if I should give it a shot. The huge upside of the torsen-style ones is they're basically maintenance-free. Just change fluid once in a while and ignore it. If the WaveTrac really gets rid of the Quaife's main negative point, how much is all that 1.5-way-clutched maintenance worth to me? Does the 1.5-way really feel/drive that much better than a torsen?
About the only thing another evening of research has sorted out for me is I probably don't want any of the Carbon options (from Nismo or Carbonetics). Once you get through all the marketing BS, the bottom line is all the Carbon surfaces do is reduce noise and maybe modify fluid/clutch life, but the metal discs perform better.