Well the max limit would be 125kk currently cause thats all your bank can hold. They should remove the max vendor price and also make it possible to get checks larger then 1kk.
only way to make 10kk checks currently would be using a player vendor and withdrawing that much gold off the vendor. Banks can only hold 7.5kk gold and you need an open slot to make a check so 7.44kk would be the max check you can make naturally by saying check xxxx