Looking for upgrade advice

Ok so here's the deal, I have a major itch for an upgrade and I finally have a little bit of income I can dispose of, and this looks like one of the best time for an upgrade as well.

So current specs: Asus n570sli MB, 4gb ddr2 800, amd x2 4000+ oc'd @ 2.3 ghz, Nvidia 8800 gts 320mb, 2 250gb hard drives, etc...

Ok so my main concerns are the processor and graphics card. I really REALLY want to get a 4870 when they are in stock. My concern, however is that my processor is bottle necking me with my current specs, and so would be even worse with a far better gpu. Also if I upgrade the processor I want to get a new motherboard, most likely an amd790 one (I know but I like the idea of having a complete system   ).

So basically my conundrum is this: Buy the graphics card now and upgrade processor/mb at a later date, do it vice-versa, or buy proc/mb and a 4850 now. Honestly I'm leaning towards the 4870, but if my proc is in fact a large bottle neck then I would re consider. Advice? Thanks in advance!