There is a link to the CEL (combined eligibility list) for PSA and PDT on your MECs homepage under documents. The list is sorted by DOH for the combined groups. It hasn't been updated since April 12' but would give you some idea of how a straight DOH merger would playout.

As a mid seniority FO at PDT I feel like I would lose some relative seniority in a DOH merge, but in IMHO DOH is the only fair option in any merger.