I have the non brushless version of that dewalt kit (DCF885 impact and DCD785 combi) and it's brilliant. I upgraded to a 2ah and a 4ah battery (from 2x 1.5ah ones). While there is nothing wrong with the smaller than 2ah batteries (1.5 and 1.3ah), you don't get the charge indicator on them so can't easily tell how charged they are. That said if you are upgrading from old ni-cad tools, even if the only drill a few holes straight from the box you will still be amazed as old ni-cad cordless generally needs a charge before doing anything!
Dave
Dave