Need advice buying custom-made computer

I customized this on avadirect for 670 dollars roughly:

COOLER MASTER Elite 330 Black Mid Tower Case, ATX, No PSU, Steel
ANTEC EarthWatts EA500, 80 PLUS®, 500W, 24-pin ATX12V EPS12V, Two 6-pin PCIe
GIGABYTE GA-M68MT-D3, AM3, nForce® 630a, DDR3-1666 8GB /2, PCIe x16, SATA 3 Gb/s RAID 5 /4, VGA, HDA, GbLAN, mATX, Retail
AMD Athlon™ II X3 450 Triple-Core 3.2GHz, AM3, HT 4000MHz, 3x 512KB L2 cache, 95W, 45nm, Retail
CRUCIAL 4GB (2 x 2GB) PC3-10600 DDR3 1333MHz CL9 1.5V SDRAM DIMM, Non-ECC
SAPPHIRE Radeon™ HD 5770 850MHz, 1GB GDDR5 4800MHz, PCIe x16 CrossFire, 2x DVI+HDMI+DP, Retail
WESTERN DIGITAL 500GB WD Caviar® Blue™ (WD5000AAKX), SATA 6 Gb/s, 7200 RPM, 16MB cache, OEM
RAID No RAID, Independent HDD Drives
SONY AD-7261S Black 24x DVD±R/RW Dual-Layer Burner w/ Lightscribe, SATA, OEM
INTEL PWLA8391GT PRO/1000 GT Desktop Adapter, 10/100/1000Mbps, 32-bit PCI 2.3 33/66 MHz, Full-height, OEM
MICROSOFT Windows 7 Home Premium 64-bit Edition, OEM
WARRANTY Silver Warranty Package (3 Year Limited Parts, 3 Year Labor Warranty)

Any suggestions for changes I could make? Keep in mind I have limited options I can use. http://www.avadirect.com/custom-pc-configurator.asp?PRI...

Is the extra 70 dollars worth the jump from an ATI 5670 to an ATI 5770. I know the automatic answer is always always "Pick the more expesnive one!", yet consider that I will only be using an old 17 inch monitor at 1280x960 resolution. Won't that extra power be wasted? I also heard due to only being 128 bit something, the 5770 occasionally (uncommonly) stuttered.

Will this run shogun 2 smoothly at high settings?

Will this run BF3 smoothly at low settings?

Other than that, were all the components I chose of a high quality and good brand?

Thanks.