I found the main performance increase beyond 5,000rpm. As I got the Kit fitted when I bought the car (bold move, eh?) I ended up negotiating quite a bit of the price of car/kit together. Research did say on numerous occasions that its £3,499...however this needs citation as I may have either misheard/got confused/missed out some T&Cs.
Yes the pirellis dont generally hold corners when you're powering over them but they tend to be quite a "soft" tyre. Has anyone had any other tyres fitted?