I'll look again, as should others, to see whether the limit is a payment of $2,500 yielding 5K miles in all, or $5,000 yielding 10K miles in all. I do believe it is the former.

I am not clear what you mean by "$7K + bonus = 12,000mi." One can pay as much in taxes as one wants if they are willing to pay 2.49% for the miles. The question is how large a payment can one make and get "double miles," reducing one's cost to 1.245 cpm. Personally, I have no interest in buying miles at 2.49 cpm, though that might work for some premium international awards; I am very interested in purchasing very large numbers of miles at 1.245 cpm, though.