With the Berk Technology 135i, we saw an improvement of about 2 seconds per lap at Buttonwillow Raceway when going from the runflats to Toyo R1R street tires.
We are now running 2:03's at Buttonwillow on Dunlop Direzza Star Spec street tires. To put that time in perspective:
Driven by Steve Millen:
Corvette Z06 = 2:01
Lotus Exige S = 2:04
997 GT3 = 2:01