Draw distance is a hog and if you want to have it all the way up, there is not much you can do but buy some hardware. Make sure you have light shafts and water to their lowest level. If you cant get an acceptable frame rate with everything at low/disabled except draw distance and projected textures. head on over to Newegg (or your favorite comp hardware vendor) and plan to spend a few bucks. I You can get workable results out of WoW in the $150 range and perhaps a little lower than that.

turn the setting down a bit, iven if it says "recommended" go just a little below that, also some addons could be causing the low fps

As a corollary to this, can anyone help me understand why I'm getting massive fps spikes in certain dungeons? Just bought a new machine and not even the old one had this problem. Basically, it'll freeze the image for 2-5 seconds and then burp it all out almost instantly. Happens quite frequently (2-3 times per heroic) but hasn't happened in non-instanced areas.

Turn down shadows and sound quality to minimum then up them a bit at a time till you find a sweet spot. I found on my rig that shadows were the killer.

What's really fun is being so minimized in every category that Blizz won't even let you run addons. And still 20 fps, at best.

Jestin,
Usually that (but by no means always) means an addon is behaving badly or a config variable gone wonky. Even if it was fine on your old system, it might not be fine on your new one. Or an update could have changed things.
To test if that's problem, rename your Interface and WTF folders (which will temporarily pretty much make WoW run as if it's a clean install) and see if the problem continues. If it stops, then it's a tedious task of turning them on a few at a time and resetting up the settings and narrowing down which one is causing it. If it doesn't solve it, delete the new Interface and WTF that WoW will have created and rename the folders back to their original names and you'll have everything set back up the way it was.

If it's not an addon or a bad config setting, then it's probably something with your system. Unfortunately, tracking it down in that case is a lot more difficult. The easiest things are to make sure you have all the latest drivers and OS updates, if you have a DX11 video card enable DX11 by adding SET gxapi "d3d11" to your config.wtf file, if you use Win7 turn off automatic wallpaper changes in your theme and if you run WoW in a window try running it in fullscreen instead.

From there you might look for BIOS updates for your mobo, disable unnecessary windows services, run memtest86+ to check for faulty RAM, stress test your CPU and RAM with Prime95 to further check for hardware issues, run Furmark to stress your graphics card, turn off features such as Turbo Boost (the shifting can cause lag spikes if it's implemented poorly by your Mobo), there's tons of possibilities and if you aren't very technically savvy, you might end up causing even more problems than you fix (especially if you start digging around in the services or your BIOS, the testing should be fine as long as you keep an eye on things)