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.

Get the CPU/mobo/cpu cooler. Get the e8400 and OC it.

I would agree with the PII 720 recommendation (I own one). However, with games like WoW and EVE 2 vs. 3 vs. 4 vs. 8 cores doesn't make as much difference. Unless you game with 12 programs running.

e8400 if you have to or are more concerned with max clock speeds, 720 if you want the best value/monies. The other benefit is the LGA775 socket is being phased out while the AM3 socket is being phased in.

CPU's don't vary in price and performance nearly as much as GPUs do. Today the 4890 is high end, in 2 months it could be budget (you get my drift). Best to wait to buy the GPU as the final part in a drawn-out build like this.