Keep in mind that if the expenses you pay with that card decrease, so will the cash back.
Personally, I would never add a number as low as $600-$800. That's slush money, as far as my planning goes. For my comfort levels, if I am cutting it that close, the I would be worried about every penny, every flat tire, every increase in the cost of milk, and anything else. So I'd not consider something that small at all.