IMO Hasten is too useful to drop, it gives extra recharge on Energy Absorption, Hoarfrost, Hibernate and your attacks.
My gut feel would be Build Up is the most missable, I wasn't very impressed with it on Golden Golem, a 80% damage buff available for 10 seconds every 30-45 seconds ( with Hasten ) is about equivalent to a 20% damage buff or a 12% increase in damage if you 3 slot all of your attacks for damage. I found that it didn't always allow me to get all my attacks off before it ran out, however this may change when they remove the pause in FSC. If you can get more than 2 AoEs off in the duration it may well be worthwhile though.
Icicles fully slotted will increase AoE damage by around a third, it does about the same or more DPS than each of the Fire AoEs. It does small amounts of damage but it does it every 2 seconds.
Incinerate and GFS will boost your single target damage to a respectable level, before them I found Golden Golem's single target attack damage was severely lacking. The 2 of these will both probably increase your single target damage output by a factor of 3-4. If you don't mind having problems with bosses and AVs ( without good damage support ) these are droppable. I generally use GFS, Incinerate, scorch and FSC when fighting AVs. I sometimes even use Boxing.
@Unthing ... Mostly on Union.
Out of that list, ditch Build Up.
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Build Up it is. I'm actually relieved as I feel it's less fun a power than the others, must have been stuck in Blaster mentality that Build Up was essential.
Nothing else I have is even remotely skippable, Ice seems very power hungry. In theory I could take SS as my travel power and save a power choice but anyone who has teamed with any of my melee characters knows I need my Combat Jumping. 
I only even really used Build Up for Alpha strikes and against AVs - I'm sure it does make a difference but not big enough to justify taking it over any of the other powers in the sets.
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Right, here's the build up to level 40. I'll swap some damage/recharge for endrdx if needed but so far (at level 15) endurance is really pretty good as long as I don't try to solo or fight with Sprint on. That's why I feel reasonably confident to push Stamina to 22 and get Glacial Armor earlier.
Slotting was a bit of a pain as I had plenty of slots in the late teens and way too little in the 20s.
Any comments? I'm a bit unsure about slotting for Energy Absorption. I guess Hibernate doesn't really need slots?
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Exported from Ver: 1.7.6.0 of the CoH_CoV Character Builder - (http://sherksilver.coldfront.net/index.php)
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Name: Emma Grace
Level: 41
Archetype: Tanker
Primary: Ice Armor
Secondary: Fiery Melee
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01) --> Frozen Armor==> EndRdx(1) DefBuf(3) DefBuf(3) DefBuf(5)
01) --> Scorch==> Acc(1) Dmg(17) Dmg(17) EndRdx(37)
02) --> Chilling Embrace==> EndRdx(2) Taunt(15)
04) --> Combustion==> Acc(4) Dmg(5) Dmg(11) Dmg(13) EndRdx(13) Rechg(15)
06) --> Hoarfrost==> Rechg(6) Rechg(7) Rechg(7) Heal(9) Heal(9) Heal(11)
08) --> Wet Ice==> EndRdx(8)
10) --> Taunt==> Rechg(10)
12) --> Combat Jumping==> DefBuf(12)
14) --> Super Jump==> Jump(14)
16) --> Hurdle==> Jump(16)
18) --> Glacial Armor==> EndRdx(18) DefBuf(19) DefBuf(19) DefBuf(21)
20) --> Health==> Heal(20) Heal(21) Heal(40)
22) --> Stamina==> EndMod(22) EndMod(23) EndMod(23)
24) --> Hasten==> Rechg(24) Rechg(25) Rechg(25)
26) --> Energy Absorbtion==> Rechg(26) Rechg(27) Rechg(27) DefBuf(29) DefBuf(31) DefBuf(33)
28) --> Fire Sword Circle==> Acc(28) Dmg(29) Dmg(31) Dmg(33) EndRdx(33) Rechg(40)
30) --> Icicles==> EndRdx(30) EndRdx(31) Acc(34) Dmg(34) Dmg(34) Dmg(36)
32) --> Hibernate==> Rechg(32)
35) --> Incinerate==> Acc(35) Dmg(36) Dmg(36) Dmg(37) EndRdx(37)
38) --> Greater Fire Sword==> Acc(38) Dmg(39) Dmg(39) Dmg(39) EndRdx(40)
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01) --> Sprint==> Empty(1)
01) --> Brawl==> Empty(1)
01) --> Gauntlet==> Empty(1)
02) --> Rest==> Empty(2)
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The late teen slotting problem can only be done one way, using a respec and getting Health at 16. Of course that would mean missing a useful power until 18/20 so it probably would not be a good idea.
For Energy Absorption I would slot Recharge and def. It becomes perma with 1 recharge and starts double stacking with more ( always a good thing ). So I would slot 1 recharge first and then decide to continue on recharge or add def depending on whether you need endurance or not. Personally I would try and slot it ASAP. It's a bit of a shame that there are so many six slottable powers in the late twenties/early thirties, I had the same problem though.
As for Hibernate, I haven't really decided on how to slot it yet. I think I only have the default slot, but I can't remember whether it is slotted for recharge or healing. I generally only use it every 2 minutes when Rage crashes to top up my hitpoints, or to wait for Hoarforst to recharge when I'm over my head. It does let you tank over your safety limit quite considerably.
@Unthing ... Mostly on Union.
I'm trying to figure out a build for my Ice/Fire tanker and no matter what I do, I'm one power choice short pre level 40. So what do I drop?
Icicles
Build Up
Hasten
Incinerate
Greater Fire Sword
I think it's going to be either Icicles or one of the ST attacks. I'm tempted to drop a ST attack as I really like the look of Icicles and it's an AoE geared build, but what do you think? It's my first tanker so I'm not quite sure what kind of ST damage output I should be expecting. Dropping GIS or Incinerate would leave me with just two ST attacks.
I'd probably pick up whatever I left out sometime in the 40s.