I think I just remembered one answer. I'll be changing water frequently, and a 29 would have less to change, but I'd probably be lowering the level in the 55 anyway.
[SIGPIC][/SIGPIC]Bill.
I often breed pairs in 75 gallon tanks. If I was setting up a bank of tanks for breeding I would use 29's more for space in the fish house more any other reason. Having said that new pairs, albino's, or some PB's do better in smaller tanks because they can suck at attracting the fry to them....but I have also bred very clean PB's in a 75 without issue.
-john