OK, so we're getting closer to the point where the new car makes sense. Still not there yet.
See how the math works for yourself:
http://spreadsheets.google.com/pub?key=pe_B8vgjx0mQTNyioMLMZfwPlay with the numbers, or download it yourself.
If you want to edit the document, PM me with your email, I'll invite you to collaborate on the doc.
Excel version attached to this message.