Your second drive having two letters allocated probably means that it has two partitions. Was it formerly the primary drive in a computer? Quite often manufacturers have a recovery partition. I think the only way to eliminate the E partition would be to reformat the drive, but that would lose all the data on it.
What's wrong with the optical drives being G and H? Some people name them Y and Z or something like that so that they don't get changed if other devices are fitted.