Best Processor For Dell Dimension E521 <Advice Needed!

I have a Dell Dimension E521 [3GB Ram, AMD Athlon 64x 3800, 500 Watt PSU, 9800GT VGA) and I am looking to upgrade my processor. I need to know which is the most powerful processor that could be installed in my computer. I like multitasking - Internet, Movies, Documents all while defragmenting my computer (Well not that last part, but you catch my drift.)

I need to know what is the best option for a processor that will be perfect and practical for my Dell E521. Also, should I upgrade to 4GB of ram? Computers now a days come with a 8Gig memory capacity.

I appreciate any help, thank you.

Technical Details: AMD Athlon 64 X2 Dual-Core
Model: 3800+
P/N: ADA3800CUBOX
Stepping: F2
Frequency: 2000Mhz
HT Speed: 2000
Voltage: 1.30V/1.35V
Max Temp: 131 to 158 degrees F
Thermal Power: 89W
L1 Cache: 128KB x2
L2 Cache: 512KB x2
CMOS Technology: 90nm SOI
Socket: Socket AM2
AMD64 Technology: Yes
Simultaneous 32- & 64-bit computing: Yes
HyperTransport Technology: One 16x16 link at 2000 MHz bidirectional
HyperTransport Technology I/O Bandwidth: 8 GB/s
Integrated DDR Memory Controller: Yes
Memory Controller Width: 128-bit
Type of Memory Supported: PC2 6400 (DDR2-800), PC2 5300 (DDR2-667), PC2 4200 (DDR2-533), and PC2 3200 (DDR2-400) unbuffered memory
Memory Bandwidth: Up to 12.8 GB/s
Total Processor-to-system Bandwidth (HyperTransport plus memory bandwidth): Up to 20.8 GB/s
Warranty: 3 years

Also, since there seems to be a three year warranty on the processor - could I just call AMD and tell them my processor is malfunctioning and I need a new and would like to upgrade? Just a thought - It might save me a bit of cash.

Any question or comments can be directed to PaxamK@GMail.com

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I know this is an old thread but what processor did you end up using?