Slotting for Storm/Psi

Just a couple of powers really have me stuck. I'm not sure which IO sets to use or even if I should use sets or just stick with regular IO's. The powers are..

Will Domination - ??
Vengence - Yes, not just a storm power.. Still unsure how to slot it
O2 Boost - Miracle? Numina? Heal IO's?
Snow Storm - ??

She is Storm/Psi/Elec. As of level 44 she is able to solo, FINALLY. Mostly she is there for support of a team, as I have few slots given to my attack powers.

And feel free to give advice on any powers in this set. I'm hardly a slotting guru.

In general, I try to have certain goals in mind when making an IO build, and the slotting of various powers will be determined by those goals. There is seldom an absolute theoretical best slotting for a power; it depends on what the goals are.

For example, I've made characters with the defense soft cap in mind (for one or more postions or damage types); characters trying to pile up large End and recovery bonuses, damage bonuses, regeneration, or recharge; sometimes I make combinations of the above ("What's the best regen I can get on a soft-capped SR Scrapper without giving up much recharge?")

You can make a mishmash of different set bonuses and you will be stronger than a non-IOed character, but generally individual set bonuses are small, and the strength of specialist IO builds is in piling up many smallish bonuses to an impressive end result.

Do you have a goal, or something you'd like to push for in set bonuses? Telling us will help us help you.

If you don't have a specific goal in mind, you might do better by frankenslotting and ignoring set bonuses. IMHO really good powers are often better off frankenslotted to get the most out of them; trying for set bonuses can wind up costing you key enhancement values (for example, there are some nice set bonuses in expensive sets that nevertheless leave you with low values for endurance reduction or recharge. I'd hate to have only 30-40% recharge in Tornado in pursuit of another small set bonus.) Sets that have a lot of good powers (as opposed to thowaway powers) are good candidates for frankenslotting; I consider Storm to have a lot of good powers.

Goals would be.. Recharge and end usage. Those tend to be my two biggest enemies when I'm playing. 4 or 5 toggles running, and then attacks, she suffers. I need to keep some powers, like snow storm, able to slow everything, so keeping that with SLow IOs may be best.

I dont need her to be a blapper (Ha! Like it would even be possible!) and I don't expect her to deal a lot of damage. But it would be nice to be able to do something more than lightning storm and snow storm and then sit there and wait till the bad guys are killed by the rest of the team.

Well there are two main ways to build with set bonuses. You can either go for heavy recharge bonuses to get more LS, tornado, and FR (this would be the team build preference). Or go for a high defense (My secondary build is soft capped to ranged and aoe damage) but at the cost of utility. I would advocate focusing on recharge bonuses, although I tend to put off heavy slotting until lvl 50.

Will Domination:
Obviously you want to focus on damage here since it is one of your heavy hitters and the sleep will be too easily interrupted by freezing rain. I would recommend going 5 slots of decimation for the -recharge bonus. If you are having serious endurance trouble you could slot thunderstikes instead. After damage, the importance of endurance, recharge, and accuracy will depend on your play style (how often do you attack, how low do you run on endurance, how frequently do you use freezing rain, do you run tactics?)

O2 Boost:
depends on your play style. Is this a power you use all the time, or only through out occasionally? How many slots are you looking to spend? Again 5 Doctored Wounds will give you the recharge bonus, if your planning on spending fewer slots, miracles and numinas are comparable in my book (although obviously don't slot the uniques) depending on your endurance situation. Also at 50 consider the Hami Heal/endurance depending on the frequency with which you use O2 boost.

Snow Storm:
I recommend devoting two slots to snow storm and fitting it with a pacing of the turtle and a tempered readiness end/recharge/slow, although depending on your endurance situation and the frequency with which you use it, you may need to go heavier on the endurance.

I run tactics. I'm pretty much centered around team build with this, so the end usage will be the key. O2 boost us used as needed. I don't rely on it for anything. I drop Freezing Rain and Lightning Storm constantly, and Snow Storm on any boss/EB/AV I meet. So It looks like recharge and any helpful end bonuses I get are the winner!

I'm of the opinion that storm defenders don't need to slot for slows since they reach their slow cap so easily (freezing rain + snow storm = slow cap on most enemies). I agree with you that slow/end/rech is the way to go if you do slot for it though.