After playing all variations of stormies, and taking a storm/dark to 50, here's my 2 infl worth.
Storm/dark is like a swiss army knife. Actually, it's more like a swiss battle axe. It has a tool for almost any situation, whether it's dealing damage, mitigating damage, or healing damage. It does, however, have a few holes.
One hole is handling LTs and bosses. Stacking Dark Pit and Thunder Clap will disorient both, but they will recover pretty quickly... usually before you take care of them. I have found that Psy Mastery fills this hole beautifully.
Domintate will take care of LTs with one shot. Bosses? Either stack Dominate, of hit them with Telekinesis. While soloing, you can easily hand 1 boss (TK), at least 2 LTs (Dominate), plus their minions (DP & TC).
Another advantage is that you don't have to get into melee range, like when you stack Thunder Clap. Oh... Dominate & TK work better with Hurricane than TC, too.
If you're worried about losing out on the Dark Mastery Pool, don't be. I tried it out on test, but found it rather disappointing. Oppressive Gloom has a pitiful radius. Do you really want to get that close to the bad guys? You're a stormie for goodness sake! That's what Hurricane, Lightning Storm, Tornado, and Gale are for - keeping guys OFF of you!
Dark Consumption - same thing - pitiful radius.
Soul Drain might be good, but it doesn't sound like it's worth it to give up the control from the Psy pool.
My other recommendation is TP Foe.
TP Foe is great for cherry-picking foes from a group. LTs sometimes draw aggro from the group, but you're usually safe with minions. (Please note that you can't TP guys that are too difficult - You can TP an orange minion, but not an orange LT. You can TP a yellow LT, though.) So, you can use this to thin out groups before you go in for the kill.
HOWEVER, the coolest part of this is where you're TPing these unlucky foes TO - right into the heart of the storm. I assume you do have Lightning Storm, Hurricane, and Tornado waiting for him in the corner that you drop him in... right? This is great for taking care of pesky guys like sappers.
Finally, we all know that Storm causes a lot of scatter. Even the best of us let one get away from time to time. Suppose, for example, that Tornado knocks a guy out of range. Tornado will come back to you, and the bad guy will eventually recover and open fire. That's not good. So, what do you do? Running over there isn't always a good idea. Plus, you still have Lightning Storm running over head. It would be a shame to waste it. Ahhh... if you have TP Foe, though, you can just grab that poor SOB and plop him right back down into your zone of destruction. LS will open up, and Tornado will lock on again.
Finally, how many times has your knockback/up/down/sideways gotten a guy stuck in the ceiling for a wall? You know... the ones you can't target? You can grab him with TP Foe and clean up your own mess. Problem solved.
Good stuff... good stuff. I recommend 1 acc, 1 range, 1 recharge. With one recharge, TP Foe will come back just as you finish the first guy. Range is great, as it decreases the odds of pulling the rest of the group. With 2 ranges, you can pull a guy when he so far away that you can't even see him (or just barely), but are still locked on.