We run 25 man normal ICC on Tuesday evenings, a totally seperate lockout, aimed at gearing up new raiders and giving people experience of ICC at a slower pace than on Team Donkey runs.
We have a description of our raid structure available on these forums, Team donkey is a hardcore progress focused 25 man raid.
We are unusual in that we are able to run 2 25 man lockouts per week with more than just alts.
As you say, we have 682 members, and this means that we cannot structure 25 man runs around 1 person. if you are not able to raid on Tuesday evenings when our second ICC 25 lockout runs then that is regrettable.
The problem is that we have people raiding ALOT each week, between 10 and 25 man runs on mains and alts, and there is simply no time to put together a third ICC lockout with enough people geared for it.
There will not be a 40% buff, and Late Night ICC and Saturday's Team Super are both getting fairly close to the Lich King, so it would be worth persevering with those groups if you just want to kill Arthas.
My Gear Score is higher then some other people who constantly get in
Gearscore is utterly meaningless and does not play any part in how we select our raid teams