Many in the know say, "Dont mix and match". Discard what you had and buy all that you need. Usually if you dont mix and match, the computer works just as fast as the slowest ram will allow.
HIS HD Radeon 7770 GHz Edition iCooler Core: 1000MHz
Sound Card
Realtek HD Audio
Monitor(s) Displays
Dell E2311H DVI/VGA 5ms response, Full HD
Screen Resolution
1920x1080 @ 60Hz
Hard Drives
320GB Seagate Barracuda 7200.02 SATA II
PSU
Cooler Master Extreme Power Plus 700w
Case
Lian-Li PC-6010 With Side Window
Cooling
Aywun A4 80mm fan
Mouse
Logitech K120 Wired Mouse
Keyboard
Logitech K120 Wired Keyboard
Internet Speed
802.11B/G/N 17Mb/s
Other Info
AMD Catalyst 12.6
Thomson A/B/G/N Router
LiteON CD/DVD Player
GAME PERFORMANCE:
Battlefield 3: 41 FPS High 1x AA @ 1280x720
Mass Effect 2 and 3: 60 FPS Highest 4x AA @ 1920x1080
Counter Strike Source (and other Valve games):
300 FPS (max FPS in game) Highest settings 8x AA 16x AF @ 1920x1080!!!