IMHO, you'd probably want to start from scratch and build something new, i don't think any of your current rig would be 'upgradeable' that is anything you do replace would simply not pick up the slack of the remaining parts, what you want is a new everything if you have the money for it.
wouldn't really know where to start if you wanted to do it piece meal, if you replace the GPU with a newer one your cpu will still be under performing, if you replace both the gpu and cpu, you'd need a new mobo, (which is half the pc right there) and if you did that you might aswell get at least 1600 ram. on top of that you'd probably want a better power supply to compliment the new parts, and then storage devices with better read/write speeds.
then again you should be getting at least 30fps in wow in a raid setting with that pc. you could just go with a psu and gpu upgrade. which wouldn't be as painful as replacing the whole thing but it wouldn't give you as much future proofing either. also blizzard have stated that the performance loss with the new models isn't that much. if i remember the blue post correctly it was saying something like a 5% difference. which would be like a frame loss of 1 if your getting an average of 30. as ppl say wow is cpu intensive so buying a newer gpu might not really have that much of an affect on your average frame rate. (although it would benefit other games that do utilize gpus more)
to play wow on ultra in a raid setting averaging over 60 fps you'll want an overclockable i5. mainly because those chips have much better single core performance than any amd chip.
like this
http://cpuboss.com/cpus/Intel-Core-i...enom-II-X4-955 see single core performance. thats where you get higher frame rates in wow.
what you need to state is your budget so the tech savvy ppl on this board can find parts to fit your budget and would make the most difference. also country and resolution help with the part picking. if i were in your situation and was looking for a really decent upgrade and cost wasn't an issue, it would be a cpu/mobo/ram bundle like
this and i'd buy a new gpu, case, psu and storage devices separate. in total you'd be looking at about £800 or $1300. for a pc that runs wow at a consistently high fps and also runs other games well too.