I say TAMah, and I like it better than Tamara or Tamsin. But I think of it as a river, not a biblical reference. Some biblical names are good, some are so-so, some are dreadful and some are associated with the fanatical fringe and therefore distasteful to me.
I liked the flow of Tamar Celeste, but I don't enjoy Celeste (Queen of the Elephants and my friend's cat) so keeping a good rhythm we could consider Tamar Louise, Tamar Suzanne, Tamar Eleanor, Tamar Clare, Tamar Angela. Or Tamar Susannah, Tamar Talitha or from the other end of the Bible, Tamar Christine. I didn't like an R- name following Tamar, so that cuts out Rebecca as well as Rosalind and Rosemary.