Most like will wait. If it is months I will impatiently wait. If scheduling or delays happen, I am keeping my options open for now. Really want the gt even though I give up 20-30 miles.Why not just wait for the GT? It's just an 6 extra months, right?
Alex's rule of thumb, for cars on average, is 11% lost when you drive off the lot, plus 15% for each additional year. Due to tax incentives that are separate from the dealer transaction, I'd subtract another $7500 from the sale price before taking off that initial 11%.
So figure you might be out an additional $5-10k as the cost of borrowing a Premium MME for 6 months? Anyway, just a rough number to compare against your other options.