In my opinion if you dont mind paying 20k + euros for a 600 hp kit,,,, i would go with the RS tuning 600 package without the catalyic converters 6155 Euros...

And then buy the Secan cores for 14000 Euros , i think you can get them for a better price from cargraphic...

total 20155 Euros.....

I think it will be a better deal than opting for the 22500 Euro.. Manthey package.. plus you get the secan intercoolers..

I already orderd the same power kit for my 997 GT2... deleting the catalyic converters will reduce EGTs, IATs , and increase overall efficiancy....

Thats just my 2 cents..

Good luck...