We'll I've tried the stock clutch unit, I'm moving over to the torsen unit now from a miata, but considering buying a OS giken unit to slap in there maybe later on ... what do you track guys run and why?

 

I'd think you'd be better staying with the clutch-type stocker - it can be rebuilt or extra plates/shims added to make it lock more aggressively. Torsens don't really wear and are quiet and smooth in operation, all desirable for OEM or light track work, but if you lift/unload a rear sufficiently, they essentially become an open diff.