2 stage build, which to do first?

My current fail system is a p4 3.08 hp thing, I've changed the video card to a 9400gt and the power supply to a 430watt thermaltake.

I currently have already in my possesion the case for my new rig, an Antec 900.

Now, my new proposed build is as follows:

MB: Gigabyte EP45T-UD3P
CPU: Dual Core E8500
RAM: 2x2g DDR3 1333mhz
PSU: Coolermaster RealPower Pro 750w
GPU: XFX 1gb 4890

Im also planning to add a sound card and cpu cooler at a later date from the original build.

My question is this, tomorrow I want to go out and spend some cash on my new rig, im not going to be able to afford the whole thing but I can probably get MB/CPU/RAM or PSU/GPU, with whichever one I dont buy following next week. My games of choice atm are WoW and EVE. Which immediate upgrade will net me better fps? Upgrading the MB/CPU/RAM into the new case with the old (430w) PSU and 9400GT GPU? Or, buying the new 750w PSU and XFX 4890 and transplanting the old mobo etc into the new case (just as a bit of a dress rehearsal, and for better cooling)

At the moment, in 25 man raids my FPS drops to a profanity worthy 5-10 FPS, best I will get anywhere is around 25 sustained(max 60 rarely).

The old motherboard is a hp store bought POS, which I hear is impossible to overclock. The 9400GT is already overclocked with Rivatuner...but the CPU is definately a bit of a bottleneck too my g15 LCD performance monitor tells me im sitting on 100% CPU usage all the time in WoW.

Oh, and if I've made any monumental errors in that list of parts, or missed something important, a heads up would be nice too =) All my bits will be coming from MSY, coz I can spit on a shop from my front doorstep, and I dont know anywhere else cheap in adelaide.

+1 to that suggestion. It would be more beneficial I think. So if you can wait just a little longer for a nice graphics card and psu then the cpu/mobo/cpu cooler will be a better first pick.

Or if you want you can always wait a little longer and save up and buy everything at once.
Did you ever take a look at the x3 720be from AMD? It is a little cheaper and performs about the same as an e8400 if not a little better. Take a look around and research it. It also has 1 more core then the e8400 so it could be more beneficial for multi-tasking. It can get a pretty nasty overclock just like the e8400 too.

In the end it is all up to you but I would pick an x3 720 over an e8400 anyday, especially considering the price.
x3 720 http://www.newegg.com/Product/Prod [...] 6819103649 $140
w/ this mobo : http://www.newegg.com/Product/Prod [...] 6813128384 $130

Yup I own one as well. A very nice chip. I am running mine at 3.6ghz and got it to 3.8ghz stable with a full load temp of 45C and 28C idle. If you still want to buy part of the build now and the other half later I agree with drunknmunky on getting the CPU/MOBO first.

And again you already know my recommendation on those in the first post!