Did you know that YoYo Loaches ( Botia almorhae
) get 6 inches long? Or is this not the variety you are speaking of? Just to be sure.
Ive never had them before so cannot give a personal experience evaluation, but I have seen them in LFS and have always been taken at the active nature of this fish. 5 really active fish that get 6 inches long in a 20 gallon tank just appears to me ( again, not having any experience with them) as a very poor environment.
The 55 gallon for 5 YoYo loaches is the better option, assuming we are speaking of same species.
Here are some links that will give you a more informed opinion:
Barbs ( in which there are many species) would work ( For example: Tiger Barbs (Systomus tetrazona
), Odessa Barb (Pethia padamya
), --- as long as kept in sufficient numbers) for the upper half of aquarium in 55 gallon.