Multi-box tanking gear and talent spec

Hey all, so glad I found this site as it's made things much easier at times for me when it comes to decisions.

Anyway, I currently have a 70 holy paladin that I've played since vanilla live and raid with her, but I have recently started up a 5-man multibox team for grinding instances to farm rep, shards, gear etc when I'm not raiding.

My 5-man recently hit 70, with a group makeup of Prot Paladin, Holy priest, Elemental shaman and 2 fire/arcane mages so now I'm looking at starting to work instances and gearing up to the best gear I can before WotLK comes out.

My paladin is http://armory.worldofwarcraft.com/character-sheet.xml?r=Proudmoore&n=Smara and the talent spec is what I thought would be the final spec for him but after reading a couple of threads today about heroics and going for defense vs mitigation I'm wondering if I would be better off dropping the 5 points in anticipation and putting them into improved devotion aura instead?

My initial thoughts were that I wanted to get to 490 defense and so anticipation would be the best place to put the points but now that I am at 70 and see I am around 450 defense with my bracer still to get +12 to it (and other enchants/inscriptions over time as I gear up) I'm begining to thing that respecing and moving those points to imp dev will provide a better benefit to me in the long run, especially given I don't have to worry about uncrushability with this character until after WotLK drops and bosses possibly get to the +3 level mark.

On a second note, again given the circumstances for this character, when I look over the gearing up list I see the OP lists items for 5-mans and for raids, should I only ever worry about getting the top-level 5-man gear listed for each slot or is it worth striving for the top-line raid gear where feasible (eg for head felsteel helm is listed as the top raid item so should I worry about trying to farm mats for it or just get something like the tankatronics)?

Thanks in advance, and again to all....thanks for the information already available.

Improved devotion aura sucks. Really. Just don't take it.
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You can't take +defense stats at face value. The +12 defense enchant to bracers gives you +12 rating which translates into +5 defense skill at level 70. Therefore, take Anticipation, as that gives you defense skill. You need 485 defense skill to be uncrittable in level 70 dungeons and heroics.
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WoW is a giant math problem, and you have the wrong answer.