I feel for you.
The car on the lot sounds like a great deal and I know how tempting it can be since it is available now. A purchase like this often involves trade-offs. If the car has most of the options you want and is a good price, that needs to be balanced against the options it doesn't have and the wait time for a new build, along with the probably higher price you would pay for the ordered car.
There are plenty of people on this board who love the ride of the X3, with or without EDC. You really can't go wrong either way. This might help describe the difference between the two:
http://www.mynrma.com.au/motoring/re...mw-x3-2011.htm
Let us know what you decide!