I had a new CooperS for about 10days or so, and had chance to give it a good workout.
The engine pulls really well, and strong - it certainly feels quicker than the Clio as it will pull from lower down. Around a track, I'd expect it to be a bit quicker, but not massively so. On the road it may seem quicker than it is if the Clio driver gets stuck in the wrong gear. There's not much turbo lag in the CooperS, a little but not that noticable.
Handling wise, it is very nimble but it feels quite bulky too IMO. It did feel much stiffer than my Clio though, thats perhaps because it's 7 years old and the Mini only had 200 miles on it (over 1000 when I gave it back
). It did feel very well planted though, a little twitchy but at least you could feel it, rather than being completely numb.
Overall, I quite liked it. I liked it more than I thought I would. But there are still several things about it I didn't like - the centre console is hopeless and clumsy (despite how 'funky' it looks), the sound was pretty crappy too. If I bought one I'd have to have a better exhaust fitted as it just sounded bog standard. Gernally though it just felt like most other 'new' cars - a bit numb and more like you were sat on it, than in it.