I too find it impossible to really determine how important a particular design of a rack is as far as impact on sound. My approach has been to find a solid, stable rack that is configured the way I need it to be, and to rely on shelves and isolation gear (e.g., rollerballs) that can be added to the rack depending on the particular results obtained.
As far as a good stable rack, something cheap, like the Atlantis racks, are quite solid and easily configurable to the spacing requirements of the user. I have seen Billy Bags racks that were also very solid and stable (they come in so many varieties, including custom design, a suitable configuration should be obtainable).
As far as a good stable rack, something cheap, like the Atlantis racks, are quite solid and easily configurable to the spacing requirements of the user. I have seen Billy Bags racks that were also very solid and stable (they come in so many varieties, including custom design, a suitable configuration should be obtainable).