Hi Iain,
Welcome to S_E
I've had an Exige S 240 PP since April 2008. An Elise 111R for 2 years before that. The performance pack comes with 4 pot front brakes and braided hoses as standard. Lot's of other goodies such as launch control, full length roof scoop, RS14 pads, traction control and lighweight wheels. The power is increased from 220 to 240 with I believe a fifth injector and some ECU work. With the N/A yota engine there is 2nd cam that comes in a 6200 rpm and gives a big jump in the powerband. Biggest difference with the S/C car is that engine just pushes smoothly through the 2nd cam cut in. The S/C cars have a more linear power delivery through the rev range. Definitely better to drive on the road and on track. There are a few that will disagree with this but had a similar conversation with a certain Welsh driving legend and he agreed with me, so can't be all bad!
The Exige is a fantastic car and super quick but I miss the versatility of the Elise. It would be great to take the roof off easily on a night like tonight. If I was buying again (unlikely for sometime

) I'd go for the Elise S/C or have a katana s/c fitted to a 111R. Although I drove the Elise S/C before buying the Exige and the sloppy gearchange really put me off. I was doing more trackdays or planned to do more so plumped for the Exige. If you are mainly driving on the road go for the Elise.
If your plan is to track the car then pop down to KH next time a track day is on, you're welcome to a pax to see how the cars compare.
Whichever you go for Exige or Elise you won't look back
If you need any more info give me a shout
Cheers Clark