[Kergan]

The harder stuff gets the better the shaman will become relative to the cleric because of slow. Mobs see a big HP and damage increase when you go to Kunark. At 41 you're also at basically the pinnacle of cleric effectiveness because you have CH and the monk can probably kill at least one mob per cast. Shamans are stuck using greater healing until 53 so there is quite a bit of chain casting heals which leads to a lot less med time.

Basically, as you level up that won't be the case anymore. Plus buffs get longer duration so there will be less rebuffing, you get better cannibalizes and more effective slows. Your heals will never get more efficient than CH though, so aside from more HP on buffs slightly increasing the efficiency of CH your cleric will lose relative effectiveness to the shaman more and more each level.

Throw in epic/jbb/pet for free shaman damage, SoW, and the ability to make potions (it takes only moderate skill to make SoW and ITU pots) and I think that edges cleric rez for general utility as well. Typically as a duo you aren't going to be delving deep into dungeons or anything so your deaths should be very minimal or PVP related (no exp loss).

The final jump is the big one though at 60 when you get torpor. Also keep in mind how fast leveling is here. 41-50+ when you'll start to notice a big difference might only be 3-4 days of playing semi casually.