So on GT tracks it's great, Bedford's Sen circuit was mighty but you'll struggle more on twisty stuff like Brands where the weight of the car and the short gearing counts against you.
This is a little bit of my GoPro footage from a wet day at bedford in the IS-F
http://www.youtube.com/watch?v=glhNTnLIy4E
Not happy with that...wanted to watch more of it
It just makes me want to do a track meet even more now.
It's well worth it, I did 4 during the time I had the car. I'd say do them but that you need to pick your tracks, Bedford was great, Rockingham on the international circuit was also good - Brands Hatch on the smaller circuit was fun but not a great circuit for the car as you've not really got the chance to stretch it's legs.
Fundamentally the biggest problem i used to have was getting the car turned in, it's heavy and that shows sometimes.
But if you're going to do a couple of days a year then you'll be absolutely fine, the brakes and tyres both held up really well.
So can't remember which setting the TC was in for that Bedford day but normally I did some runs with it in sport and some with it switched off. Sometimes in sport it was a bit conservative coming out of the corners so you'd struggle a little to get the power down as early as you'd want.