The way I got Dalaran smooth is:

After 2 years of boxing, I finally made 2 seperate WoW folders.

1 folder with a WoWclient that has high gfx settings in WoW.
1 folder with the lowest gfx settings possible.

My main shaman uses the one with high settings, and the other 3 use the clients with the absolute minimum settings.

I play 4 clients on 1 comp, 4gb memory and a 8800gt 768mb vid card.

-Menthu