Looked these up while I was setting up Octopus, found them very useful for saving me a lot of effort and CPU.
Not sure about Keyclone, as I've yet to try it out, but Octopus has a nice option to manually set your own config.wtf settings for each instance. I was going to make a post asking if anybody knew any good ones I was forgetting, then saw nobody had really made a helpful compilation at all... So I'll try.

Here's the list.
http://www.wowwiki.com/Config.wtf_defaults

Octopus automatically does
accountName and gxResolution

Some of the more useful.
  • gxMultisample - Multisampling, 1-4 (I use 4 for my main screen and 1 for the 4 smaller)
  • farclip - View distance before "fog" (Have my Main at: 1000 Others: 100)
  • maxfps - Discussed often here, maximum FPS of your currently selected game screen
  • maxfpsbk - Max FPS of unselected screens
  • uiScale - Ingame UI scaling. "useUiScale" must be "1" for this to work. (Found it useful to bump this above 1 on my 4 smaller screens, and to my usual .75 on my Main.)
  • realmName - Default Realm to load to.
  • lastCharacterIndex - Which character is selected on the loading screen (press enter twice instead of manually selecting each character when they're in different orders FTW)
  • processAffinityMask <-- *edits to add this one* -- Set what cores each Client uses.

For Graphic settings beyond the basics here, just go read wowwiki, there's a LOT of them. If you want to experiment with them in game, they can all be changed at any time using /console command, Including in macros.