Well I had to add some money but I will show you different build, basically all the same but depends on your "time". Allow me to explain:
First of all, I chaged that 3 core for a dual core one. The X2 550. This is why:
http://www.legitreviews.com/article/981/13/
As you see there is hardly any difference from both. I believe it's just a waste of 20$ you could use somewhere else. Plus the 550 is a Quad core that was locked. There is a tutorial over the internet on how to unlock the 2 locked core, but it has a 75% rate of success. Use it at the end of your CPU's lifetime, When you will require more core (in 2 years I predict. LOL)
So here's your build:
Phenom II x2 550BE
GIGABYTE GA-MA790FXT-UD5P
OCZ OCZ3G1333LVAM4GK AMD Gold PC3 4GB
ASUS EAH5770
ANTEC EA750 750W EARTHWATTS POWER SUPPLY
COOLER MASTER CENTURION 5
First of all I didnt find your seasonic PSU, but im shure the antec 750 EarthWatt is WAY better.
Secondo, Go with 4GB at start. It will give you a clear advantage as many games requires around 2.5 now AND you will be able to install a x64 platform instead of the lame x32 platform. CLEAR advantage.
The pricing is a fair 779.49 But I guess thats way up your budget.
You will be getting this build for roughly 700$ If you wait for Xmas tho.. maybe less..and thats your "Perfect" build.
Now here, the MOBO is the problem. And As I never really experienced Dual x8,rumours (and few benchmarks) are saying that you dont lose THAT much of a performance, it will only bottleneck on high level GPU wich arent out yet. If you decide to believe this (It's quite thrue tho, I think Overclocking the cpu/gpu will cover up for that) Then you should get a ASUS M4A79XTD EVO
The price is now 710$ ~110$ over your first build.
The motherboard you were getting was a lame AM2+ socket. The performance you would have lost are BIG. Very big.
Of course this build is still on top of your budget, but it will enter if you change the cooler master for the antec 200.
The antec 200 didnt win the best performance budget case against the antec 300 for ONE simple reason: People didnt like the front. Thats all. It's basically the same (a little better) then the antec 300, wich is same then the coolermaster centurion 5
http://www.sohodiffusion.com/produit.asp?num=12535#noheader
The actual 200.
With the 200, the price is reduced to 696.49
Now let's talk about the PSU. You chose a 750W, and thats why I took a 750 W.
But dude, your getting POWER EFFICIENT cards, you don't need THAT much, and your FAR from needing it.
I calculated with the New egg power Supply Calculator:
a Phenom II x2+mobo+ 2 HD5770+ 4GB + DVDRW + 1HDD = 569W.
Add a 50W "In case of trouble" and your still only at 619.
So If we change that little PSU of yours, were now at 665.49. Pretty much into your budget for the money right??
Now, we reached 734.49 for the REAL PERFECT BUILD. Only 130$ over your budget, and man your getting a BIG performance for your buck.
But even the 665$ one is very good. The 734 one is just, EXTREMLY good. So your good with both builds. Now everything depends on the prices in your country, so you should probably go with the Very good build instead xD Here's the full listing:
AMD PHENOM II X2 550 DUAL CORE
ASUS M4A79XTD EVO SKT.AM3 AMD 790X/SB750
OCZ OCZ3G1333LVAM4GK AMD Gold PC3 10666 2X2GB Kit 1333MHz 9-9-9-20
ASUS EAH5770
ANTEC TWO HUNDRED GAMING MID-TOWER (or you can still pick your case)
ANTEC EA650 650W EARTHWATTS POWER SUPPLY
For a fair 650~$, this is a very good build that will prove it's power now, AND if you ever add that other 5770 for some HD5850 like crossfire. By the way, If you REALLY want the X3 tho, its just 20$ more, so it's really up to you