I'd offer the $60K for the "demo" E92 or $57K for the new E90, since both would be cash deals. Beggers (dealer) cant be choosers.
I would take the E90 for the $57K.
I took an E92 M3 demo car with 100 miles for a test drive when I ordered my car over a year ago next to the dealer's highway.... I hit the speed limiter over 160mph with the sales guy. Not that it really matters since it would still have warranty.