I'm using a hydro sponge in a 5 gallon tank. The sponge i'm using is rated for a 10 gallon. The only difference is the size of the sponge really. I have it hooked to an ancient air pump rated for 5-10 gallons. The lift tubes get kind of gunky looking and are semi-difficult to clean if you are using tannins. I'm not even sure cleaning the lift tube is a good idea or not since I am assuming the "gunk" is good bacteria. I don't know 100% what it is though. I feel i'm still new to fish keeping and still have a lot to learn.
They make hydro sponges rated for under 5 gallons I think. Jhemco sells them, I'm not sure if any are on ebay or amazon etc. Jhemco has the best selection of them by far. I'm using the regular ones since the pro sizes seem to be for bigger tanks.
Hydro sponges look kind of like little nuclear reactors in the tank. I don't find them ugly but a lot of people don't like how they look. To cut down on noise and size of bubbles I put an air stone inside mine. This supposedly makes their filtering power slightly less or something to that effect. It's doing a good job in the tank.
You can move your fish to the new tank with a sponge filter like Lebron said but you will have to keep an eye on the water quality until your sponge filter cycles. Hold onto the whisper 3i too. You may want to use it for the carbon filter at some point. (Polishing the water, removing medicine, etc. Something a sponge filter can't do.)
I'm using filter foam and those fluval edge pre filters on the rest of my tanks intake tubes. So essentially all my tanks have sponge filters of some kind in them. I managed to cycle a 2.5 gallon aqueon bow tank with the aquaclear coarse filter foam. It's ugly as sin but the size chunk I used holds enough beneficial bacteria to hold a cycle in that tank.
It takes a LONG time to cycle the filter foam, and pre filters though, and it's really easy to break the cycles once you establish them just by over cleaning the foam/sponges in the small tanks. (killed all the bacteria once before I knew not to rinse it under hot water, and went nuts and vacuumed too much of the bacteria out once with my siphon... live and learn.)
I really only swish the fluval pre filters around in old tank water to remove stuff sticking to the outside now. The coarse filter foam I leave be mostly until I notice the output of my filter declining. I squeeze lightly and swish that one in old water before re-installing too. The hydro I swish and squeeze lightly only when I notice it starts to get gunky on the outside and the output from the lift tube declines.
Sorry this was long. I just wanted to share my experience with what I had. I am new to this like I said, so take my advise accordingly. :)