Well bigger is always always better except:
The tank is for my 10 year old son & he's going to do all the routine water changes, pruning, etc. He has enough trouble getting to the bottom of the 20 high, which is the exact same height as the 40 long. Besides, his reasoning is that a 25% water change would only require two 5 gallon buckets. He doesn't want to go that big and he'd still have the same footprint and be able to choose from the many available stands for the 55 gallon.
Anyway, I called a couple of local fish only shops & one could order one for $150, which is ridiculous for just the tank. I called another & they can order it for $100. I'll talk to him tonight & see if he wants to go for it.