997S X51 tested in Autocar
It's a very short review, but it got 5 stars out of 5.
Distinctive mid range punch compared to standard S and more shove from the start, main difference is above 5000 rpm where the engine is a peach.
So nothing new, just confirmed all the other reviews.
They say the best bit is the exhaust noice, which is PSE, so that's cool.
Only problem is once you tick the option you get close to GT3 price but they still recommend it.