750 allows you to cover your opponent's max bet double with a double of your own. Your opponent could take the low, but you could retake it by surrendering. A sim is underway to answer the question of whether giving up the low to cover a double with the option of surrender is worth the risk (asked by S. Yama on another thread). My feeling is that the cost will be too high. This situation is worse than that since you need to double yourself in order to reap the benefit. If you were giving up the low in order to cover your opponent's win, with the option to surrender, then I believe that the trade off is worth it.
1000 is an improvement over 750 in that it covers your opponent's blackjack. However, I still think that the cost is too high.