The video below shows differently though as the 991 Turbo S is actually able to ultimately pull up top. Quite impressive for a stock car. What explains this? The lighter weight of the 991 chassis is definitely a factor. Additionally, it would appear at least in this video that the tune on the 997 Turbo is not the strongest. It is said to have a tune from Speed-Concept that puts it in the 565 horsepower range and the 991 Turbo S is rated at 560 stock.
Once the 991 Turbos get tuned it looks like they will be stronger than their 997 counterparts at least in tune only guise.