I'd have better uses for my $$$. Where you going to use that 5%? Can you already use the 100% you have safely and effectively? Are you that good a driver? If so, congratulations. You are in the 1% who own Boxsters that are capable of extracting the most from their car. I'm not.
And if you aren't, then spend the $$$ on high speed driving lessons. I guarantee you'll enjoy the car more after you learn its limits and yours.
http://mike.focke.googlepages.com/itisn%27tfastenough