Honestly, another effective strategy for Fenrir is the 74+ Rdm/Drk strategy.
Any party makeup with strategy can do this, but heres what I had envisioned:
75 Rdm/Drk, 65+ Whm/Smn, 70+ Nin/War, 75 Mnk/War (That's right, no /nin), 75 Blm/Whm, 65+ Brd/Whm.
Everyone goes in and melees charge up to 300% tp. Nin engages Fenrir, and everyone uses the basic Fenrir strategy (Making SURE the Rdm conserves Mp. Have the Whm concentrate on healing with the Bard backing up. Bard should bring Mp+items.) to get him down to close to his 2h hp range.
During the first part, however, whenever the Nin could manage it without risking his life, he'd throw off a Suiton: Ni to lower lightning resist. Hopefully one or two of these would hit. When Fenrir is at about 3/4 hp, the Bard would Soul Voice and start piling on accuracy and damage buffs to the monk in particular. (The blm should also always keep enough mp to throw off a Thundaga or Thunder IV. Always.)
When Fenrir starts getting real close to 2h level, the Rdm would Chainspell and start spamming Stun. At the exact same time, the Blm would hit Manafont and start piling on pure damage spells over and over again without holding back. (Thundaga III and Thunder IV being prominent, hopefully being enhanced by Suiton) Also at the same time, the Monk does 100 fists with Warcry, Agressor, Berserk (all the fun Warrior damage boosting skills) and wails on Fenrir.
The spammed stun has a good chance of interrupting Fenrir's 2h, plus he'll be all but unable to do anything for 30 seconds. If, however, he does manage to pull off a few attacks, the whm should heal whoever recieves it.
Hopefully, during the chainspell time the blm, mnk and nin will have done enough raw damage to kill Fenrir. If not, as soon as chainspell wears off, the whm runs up and uses Benediction, followed by the Nin immediately using his 2h. If your mnk and blm have done good damage, then it should finish Fenrir off.
If even that doesn't work, well, you've got your tank dead, but Fenrir should be so close to death that one DD will be enough. The Blm (assuming he's still alive) uses the mp he's saved to cast one final spell, which should finish Fenrir off.
Now, I honestly don't have any experience in a Fenrir battle, but I turned this strategy over in my head a lot and it seems like it would work. It's pretty flexible too. So long as you've got a Rdm/Drk and enough DDs, the Nin can be replaced with a Pld or the Brd can be replaced with another DD, anything.
The only major problems with this strategy is you've only got 1 tank, and you have to conserve a lot of your attacks for after the Rdm 2hs. Blms would need to conserve mp, and the Rdm would definitely need to conserve mp. Also, if the blm's or DD's spells/attacks get really resisted, then Fenrir could stay alive long enough to destroy the pt before they can recover. It's an all-or-nothing strategy.
I got the whole Rdm/Drk idea from the Summoner board initially. Fine group of people over there (generally speaking) and have a lot of great ideas.