You could try the following:
Add another hard drive to your computer and throw 2-3 of ur wow there. I added 2 hard drives and spread out my wows (main has one instance, each new drive has 2 for 5 total)

For me this changed how fast things would load when I walked around and improved performance. it cuts down on 5 wows and whatever else is thrashing the drive so much.

Again this works for me, not saying for everyone.

Also, disable extra addons or disable them if your planning to go to dalaran (annoying i know), it should help it some.

Other then that, you could do 2 at a time or something, more time wasting I know, but alot better then crawling around for an hr just to use the bank. Also make sure shadows and other video stuff is off and down. Clip plane etc.