Last date to change
Your can change colors and options up to 3-4 weeks prior to production. It sounds like your car is being built in December sometime if it is going to be here in Jan./Feb.
That being said, the order list for CLK500 and CLK320 is two different "waiting lines" if you will. Which one did you put a deposit on? What I mean is, if you put a deposit on a CLK320 you cannot change it to a CLK500 when your production spot comes up. You are either inline for a 320 or a 500. They are two different models. If you decide to change from a 320 to a 500 or visa versa you are going to go to the back of the line for that model.
Decide which one you want and make sure you are in the queue for that model. When your production spot is scheduled you can finalize colors and options.
The 3.2 V6 is fine for the coupe (although the W209 got 300# heavier for the coupes), but...
In the old W208 body, the 4.3 V8 cabrio's acceleration matched the 3.2 V6 coupes.
And in the future for resale, I'd suspect the V8 cabrios will probably do better in that regard.
and like CME said, you would lose your place in line, as this isn't like changing options, but models within the car line.


