Well I haven't put it in a tourney (yet) but I think the following is pretty powerful:
TRAITS:
See but don’t be seen
Honour your wargear
Flesh over steel
We stand Alone
---
HQ: 203 pts
Space Marine Commander
+Combi-Plasma
+Purity seals
+Acute Senses
81 pts
Space Marine Command squad x5
+2x Plasma guns
+Infiltrate
+Acute Senses
115 pts
---
ELITES: 744 pts
Devastator squad x8
+4x Missile launchers
+Infiltrate
+Tank Hunters
248 pts
Devastator squad x8
+4x Missile launchers
+Infiltrate
+Tank Hunters
248 pts
Devastator squad x8
+4x Missile launchers
+Infiltrate
+Tank Hunters
248 pts
---
TROOPS: 230 pts
Tactical squad x5
+Plasma cannon
+infiltrate
+acute senses
115 pts
Tactical squad x5
+Plasma cannon
+infiltrate
+acute senses
115 pts
---
HEAVY SUPPORT: 672
Devastator squad x8
+4x ML
+infiltrate
224 pts
Devastator squad x8
+4x ML
+infiltrate
224 pts
Devastator squad x8
+4x ML
+infiltrate
224 pts
---
ARMY TOTAL: 1849 pts
24 Infiltrating missile launchers, and a bunch of infiltrating plasma. Not much you can do to hurt it.
But I have frequently played Eldar lists with
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Maxxed out Seer council
7 man guardian squad, starcannon
7 man guardian squad, starcannon
7 man guardian squad, starcannon
7 man guardian squad, starcannon
7 man guardian squad, starcannon
7 man guardian squad, starcannon
9 Vipers, starcannon on each
Wraithlord, starcannon
Wraithlord, starcannon
Falcon heavy grav tank, starcannon
And it only costs about 1850 pts.
A master, with powerfist,storm shield and bolt pistol, his command squad with champion, apoecthary and 9 marines with BP+CCW, an attached chaplin with powerfist and they were joined by the emporer's champion, all thrown in a land raider crusader.
That command squad has yet to be defeated, if thats not powergaming i don't know what is...
That's not really powergaming, in fact, it's pretty foolish. All someone has to do is turbo-boost a bunch of bieks around the access points of the LRC, put a penetrating hit on it, and boom! Everyhone inside automatically dies from disembarking within 1" of enemy models.
But even still, that's nothing. I have actually done the following with 2 FOCs:
Chaplain on bike with cup of retribution (basically a holy relic)
Librarian on bike with Book of Salvation (another holy relic)
8 man Deathwing Terminator assault squad, 8x lightning claws, furious charge
Land Raider crusader
The LRC blows smoke and moves first turn, second turn termies come out getting ready to charge. Chaplain and librarian on bikes move in and join the squad.
Then they assault. Both ICs reveal their holy relics, and everyone charges. The result? Well, to start with, the Terminators each get 6 S5 I5 power weapon attacks that re-roll to hit and wound. So that's 48 Strength 5 Iniative 5 power weapon attacks that re-roll to hit and wound. Ouch. However, in games of under 4,000 pts, that's kinda suicidal, because they'll probably get plasma cannoned the next turn and die, and htey probably won't make up for their points cost.