370hp on the Auto won't be a problem, and I have to say the efficiency and effectiveness of the new 8 speed would incline me to buy an Auto. Way better than the DCT I've tried in the Z4. Maybe I'm getting old. I've always preferred manuals, because you are mechanically involved in the driving process. Resale considerations say it has to be an Auto too. See if you can borrow one from your dealer for 24 hours. (no dealer has a manual demo!)
You can buy a BMW warranty from here.
http://www.bmw-warranty.co.uk/Pages/CarDetails.aspx