Id just save up for the 120 then swich the 40 to the sump. I think its a bit much to ask your parents to buy you a 120g setup for x mas. I bought a 125g by myself when i was about 14. I used a paper route to buy it. I also bought a beareded dragon and setup. Point is, its your hobby and imo you should pay for it and not rely on others for the big purchases. Its ok for them to help you a bit or front the money, but having them pay for an entire 120 g setup is greedy. a 120g tank alone is 200-300$, iron stand 100$,filter 100$ plus, lighting, heaters... more.Thats expecting your parents to spend over 500$ for you. My 125g tank bill for the main stuff was almost 900$ (tank iron stand, xp3, heater) then i probably paid another grand or two for more for it.