Differences among various BSPs

The global memory bandwidth does not depend on the BSP, it depends on the board; however, there is no guarantee that the BSP of a specific board would support all the memory DIMMs on the board. The a10ref board only has two memory DIMMs, one DDR3 and one DDR4. However, as far as I know, the BSP only supports one of them.

Depending on board characteristics, there are boards with support for two DDR3/DDR4 memory DIMMs, QDR memory, network ports, host channels, etc. Furthermore, the BSPs also differ in their quality, both in terms of how much area they use, which determines how much area is left for the kernel, and the quality of their timing closure, which could affect the kernel operating frequency. The quality of the BSP mostly depends on the amount of effort the board manufacturer puts on optimizing it.