I've always put the highest amount offered for a deposit, for a number of reasons. First, CC charges are easily disputed. Dealers get charged a fee, and you don't lose anything if you don't want the car. Second, credit card charges earn rewards. 5-10% back on a multi-thousand $ deposit can really add up. Or you can put it in a 0% bt card for more savings (by using their provided cc checks.)
Originally when I was going to purchase a DB9 for resale, I had asked about CC deposits, and large amounts are allowed by some dealerships. Unfortunately, the effort was wasted as the ford gt and all astons are not qualified under A-plan.