The Benz Dynamometer test was on a lwnmower engine. There is another dyno that was done on a Small Block Chevy recently and it showed a 3% torque increase above the best results from the unmodified heads.
Test1: dyno pull with unmodified heads
Test2: dyno pull with grooves only
Still, this doesn't show what the grooved engine is capable of doing. The benefits of higher compression without ping in addition to other low end torque benefits mean this is still a pretty good idea in my book.
