zebra tank size

[will74]

I have 6 zebra's in a 20 long with a fluval 405, two sponge filters, and a 600 gph wet\dry. They range in size from 2" to 3" and seem to be doing well.
My question is that I am redoing my fishroom and in order to keep the zeb's on a separate filter system I need to change tank size. My choices are a 33 gal long[48"Lx12x12], a 55 gal, and a 30 long.
What size would you guys recommend[and gals]? I was thinking of the 55 for the simple fact that it holds more water. any input?
Also where can i find some pics of breeding setups from those of you that have bred them before?

[alga]

For 6 fish I would go with the 4 foot 33. Good surface area not too tall, better gas exchange since its not overly deep and for my fish room, I try to keep 12 inch tall tanks so I can fit 4 rows of tanks