I'd go 2x8GB now, when you say 'upgrade' that usually indicates people are thinking of adding additional sticks which can be and often is problematic (even if you were to get the same exact model. The forums are full of folks that have tried 'adding' additional sticks and ran into problems, often this can be 'fixed' by adjusting voltages and/or timings but there's no guarantees this will work 😉