i wouldn't recommend increasing your return pump size, does very little for flow in your display compared to a mp40 or even a koralia, and an eheim 1262 isn't the cheapest pump out there, i would honestly go with another vortech if you feel there isn't enough flow, which surprises me 1 can't maintain in that size tank. As stated before going to an eheim 1262 will increase your turn over rate which tends to make your overflow louder, or maybe your overflow won't be able to handle it all together. I at one time tried to accomplish higher flow with a larger return pump also, quickly went back to the smaller return pump and was out the money that i could of just put towards a different powerhead.