I think you're still thinking too light... If you want a semi-locked rear I'd put in 100K. No, that isn't a typo.

Then maybe 20-40K in front which should still give enough pull in the turns without affecting the steering response. Does that make sense?
I run 100K front and 300K rear (again, not a typo) on my GTP. It never "diffs out" in a corner even if I stay on power, and has no oversteer, like it would if the front was too tight.