DB - i am quite perplexed that this reared it's head again (wish i could tell you why as well). prior to selling the car - i did do a few few silly speed runs, booting from different speeds, to see if the smoke had stopped.
all i can say is that it didn't do it then (as you have mentioned, it doesn't do it all the time) but i did check with mark (phoenix) who told me that even after booting it during his test drive - the underside of the car was bone-dry.
as for the lack of confidence - well it wasn't the reason but that i rarely got out of london hence rarely needed to give it stick. it did not stem from confidence issues as i found the car performed well enough.
i sincerely hope that you find the cause of this smoke and i hope it is a minor thing.