If I'm fighting/hunting, then I go 2d, if I'm at an RP event I use Third Dawn. It'll be interesting to see if the new 3d client can sway me to stay with the 3d
As far as lag, even when I had a normal computer I didn't have any probs when I maxed out my memory and added a 128 meg Graphic card..

Now I use a Dell XPS Dual core, so I have TV running (baseball playoffs), UO running, Outlook and Firefox, not a inkling of lag. I know, it's an extreme computer so I won't compare (Just to mnake ya jealous, it's hooked to a 32" LCD monitor that swings out from the wall over our bed. The wife watches TV on her regular TV and I get lost in my headphones and monitor.