Okay, played some but no large groups yet.
I currently have the following setting. Mind you, I custom tweak every setting based on the forum (eqiiforums) knowledge about which settings affect FPS the most.
I'm running @ 1920x1200, full-screen, no v-sync, no letterbox area.
Complex Shader is around 60 (but setting to even 150 shouldn't really affect too much).
Model Detail is .1, Particle Detail is .1, textures are all HIGH, particles are HIGH, water is set to ONCE, water interaction is off, animations are all on HIGH, flora is completely turned off (NO MOBS HIDING FROM ME).
Shadows are currently off, as I haven't had time to really evaluate them yet. But in my past experiences, having them on is a huge hit in sunny outdoor zones (antonica) but not so bad in other zones like nek where there is no sun -- but you also only get shadows in those zones from torches, etc. So I would really just leave them off unless you bed for eye candy.
My biggest concern that I haven't tested yet are the HO particle effects that are group effects. Also, certain mage and enchanter buff particles are brutal to the 6xxx series cards from nVidia, so we'll see how that goes. I may have to setup a macro that drops particles to medium for raids, along with setting zero high-detail characters on raids (which I recommend, since you're fighting and if you have high-detail toons, it always draws the nearest 3 (or your setting) and that means constantly swapping textures to make room for the current nearest toons.
Hopefully this week will see more action and I'll be able to decide on a final config, at which time I'll post screenshots of my settings.