What do I need to play The Sims 3 Pets + CC & Mods with maxed settings?

What do I need in order to play TS3 Pets + CC & Mods with maxed settings?
Below is my current system.
The Sims is currently unplayable on my comp. It takes forever to load, and when it finally does the graphics are extremely bad (no matter how high or low I have the settings), and when I go into buy mode it freezes.
Sorry for being so n00bish.
Thanks in advance for your help.
- S

Windows Edition: Windows 7 Professional
Processor: Intel(R) Core(TM) i5 CPU 750 @ 2.67 GHz
Installed Memory (RAM): 4.00 GB
System Type 64-bit Operating System
Graphics Card: NVIDIA GeForce GTX 275
 
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