This is just my $0.02, but I don't see the point of running a diff if you are going to run thicker oil than 50K (that's 50,000 cSt, just so there is no confusion
), you'll have so little diff action you might as well run a spool.
For reference, I started with 30K (30,000) and the car had tons of understeer at corner entry and had to essentially use full lock on all the turns with accompanied by lots of tire scrub.
IMHO, I think it all depends on your driving style, but my best results came when I dropped down to 10K (10,000). I think the car would have even done better with 7K (7,000), but my throttle application was not smooth enough to tame some of that inside wheelspin at corner exit.
And that's really what it comes down to, driving style. What I've noticed is that the drivers running more of a point-and-shoot line use the thicker diff oil because they have to--corner speeds are lower and you need max acceleration. The others like myself who use a more flowing line, like to use the lighter end of the diff oil spectrum.