As listed in title, are there any consequences of mixing 2 RAM kits of the exact same model, just different sizes?
Instability, BSoD's...grey hair, no hair on your cranium. You can search through our forums and you'll see that mixing and matching rams often leads to the aforementioned.
Not all ram brands use the same IC's, so you're essentially trying to run a car with mismatched tyres on all 4 corners, if and when you're mixing and matching ram kits/sticks.