I finally got to take an extended test drive in a 03 Cooper S. Thanks to Baron MINI and Lisa in Kansas City. Arrived and after she copied my drivers license, got the keys to a IB/W w/aero kit, leather, etc.
Got to drive it in all conditions: stop and go rush hour traffic, Interstate and some nice twisty roads. It was hot, around 100 F and 60+% humidity. Drove with A/C on and off. Could not get the car to stumble! This S had 2300 miles on the odometer, so I'm assuming it was an early 03 build.
My main concern has been the stumble and other quality issues. My Sales Advisor admitted that they have had some cars in with the stumble problem, at least they get points for admitting it exists.
My impressions coming from a pretty heavily modified 93 Honda del Sol:
This car is a handling machine! A little gutless below 4000 rpms, but does it ever make up for that in the corners! The car starts to push when taking corners at speed (to be expected with factory setup and FWD). A/C was a little weak, but that could be because I kept shutting it off and rolling down the window to get the most out of my test driving experience

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Overall the test drive was a gas. I'm going to wait a few months to see how things hold up and what happens to the stumble issue, but I can see a BG/B S in my future.