I only have one rack, this one, and have found that it's a good size. I have it split right now and it houses 2 medium BPs on the bottom and kenyan sand boas and a hognose on the top 3 levels. You CAN use a bigger tub for smaller snakes but you need to treat it like a terrarium setup... i.e. provide hides, rocks, some fake plants or balled up paper to clutter it up. I have hides in it now for my BPs and the hognose and they seem to make good use of them. As the BPs get larger, I will remove the hides and see how it goes. I plan on upgrading to a larger rack to house the females as adults, but this rack will house the sandboas and hognose for the duration of their lives.
Also a little plug for C-Serpents, Chris was great to deal with and I feel that his prices are great for the quality of his racks. Them coming with tubs and assembled also makes them more appealing than some other options out there. I picked up mine at a local show, so didn't have to pay for shipping as well.
Yeah I'm either going with 32 or 41 qt. If I do use the 41, I'll just put more hides and clutter.
I've done research on C-Serpents. Its one of my choices along with Boaphile and Reptile Basics.