If you're seriously considering it, I personally would go 42 Mentalism/33 Mana or 41 Mentalism/35 Mana. • The first would give you the last heal, while subspec Mana would give you the second best HoT and yellow PoM. • The second (which is what I would go in your shoes), would drop the best Mentalism Heal for orange PoM and a better DoT.
Having the 50 Mez likely isn't worth the investment in favour of beefing up your other support spec line.
i'm considering a light eld for the area mezz and nice stun. (Yep...i love trying lots of characters.) I was stunned (no pun) with how my 20 light ment did in his first few hours in THID(almost realm ranked out even though in a bad group).