You can do 5-gallon batches in the larger MLT. I struggled with this idea too. To satisfy myself, I built a second MLT from a 5-gallon round water cooler and use a stainless steel braid as the manifold. A deeper grain bed is a good thing but I'm not so sure that you can't efficiently do smaller grain bills in the larger MLT. I wanted both sizes as part of my brewery so I could use whichever MLT suited my grain bill the best. I make some high and low gravity beers, so I can choose the equipment that fits best. I don't make 10-gallon batches, so I can't tell you what the best solution there is, but I'm fairly sure the 48-qt cooler would handle a majority of the batches that size.