For 10H comps I would say you are going to have to pre arrange with whoever you are healing with how you want to run things. Generally you are going to be with a RSham due to the Lust buff, the others can all be very viable but adjusting your spec to suit the comp although frustrating is optimal. 10H Is generally very unforgiving when it comes to composition, simply some classes are needed and some are less desirable. So although double healing priest would handle the healing fine, you are losing potential buffs and hindering your raid. So in short if you want a happy day get a RSham partner, beyond that anything is viable, you just might have to be a bit flexible with how you play