1) Dark Blast at 41 because Moonbeam is the suck (it takes double the time of others snipes to activate). Slot dark blast with a set like thunderstrike if you intend to use it as a part of your attack chain. Devastation is good for the +hp too.
2) Shadow Meld at 44, it's a great panic button that's available often, it's like a defensive build up. Slot for defense and recharge (3 membrane HOs optimal).
3) Soul Storm at 47. I say 47 because Shadow Meld will help more in your survivability so I'd take it earlier than the hold.
Summon Widow is meh, I'd skip it and leave the 49 power for something else.
Awesome. Thank you very much =)
I'm 99% positive I'm taking Soul Mastery, I'm just curious as to which powers I want to take other than Soul Storm and in what order. Any suggestions?