CPU Upgrade Opinions

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Go for the processors on the top of this list

http://www.gigabyte.com/support-downloads/cpu-support-popup.aspx?pid=3798

The Yorkfield core 2 quad's are still a pretty solid processor and would be significantly faster than your current CPU. I wouldn't bother with a dual core, I would go for the core 2 quad as you will be buying second hand most likely and the price difference will be minimal. You can get a q6600 it's a good processor but it's more of an overclockers favourite. The Yorkfield's have a faster bus speed and they are more efficient.
First, GHz means nothing as far as performance.
Second the pentium 4 was a bad CPU design. Run far away. You are wanting to do a downgrade not an upgrade.

If you want an upgrade look for a higher level core 2 duo or core 2 quad that fits in socket 775
 
Go for the processors on the top of this list

http://www.gigabyte.com/support-downloads/cpu-support-popup.aspx?pid=3798

The Yorkfield core 2 quad's are still a pretty solid processor and would be significantly faster than your current CPU. I wouldn't bother with a dual core, I would go for the core 2 quad as you will be buying second hand most likely and the price difference will be minimal. You can get a q6600 it's a good processor but it's more of an overclockers favourite. The Yorkfield's have a faster bus speed and they are more efficient.
 
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