go test it on the rank 4 accessory quest. it's the toughest content we have right now...
except you JUST missed the fire one... so that won't show til next monday
as for grids, typical strategy is to try and use more assault than anything (SR and above)... but if you feel like your HP is too low, maybe one defender (hopefully SSR). stick pride weapons on there too in case your HP dips mid run (it'll start spiking your damage output). Eidolons, depends on how strong your eidolons are... something like a lv100 fenrir would definitely do more than a lv40 reiki in the case of water teams, but the elemental atk boost from reiki at lv100 would outdamage the character atk boost from a lv40 fenrir if you look at it that way.
in my case though, i haven't grinded out many SR weapons so i tend to fill the holes with the weapons boasting the highest stats since i now have quite a few lv100 and lv125 weapons. Better to have a grid filled with the matching SSR you have and the best you got of anything else if you can't fill the gaps with SR assault weapons after all
i tend to pass on info i find out for the most part. nothing special really