Grow up man. No OS is right for every circumstance. Do not throw in the ignorant response of Windows security (like it matters anyway, what are you magically going to get some virus from the Internet through your car? Oh, and Bluetooth, it's an unsecure technology anyway, regardless of OS). And no, your speed wouldn't be all that different. Windows Automotive and the full release of Windows are so disparate they're like different OS's. Please think before you fire off the cuff about stuff you don't fully understand.
http://video.google.com/videoplay?docid=-7148748849652085555